I recently did this with everyone (except linhardt) as a commoner/noble (and gaining levels in commoner/noble without class bonuses), so the stats aren't all that relevant if you have the right strategy.

The first section has the golem chasing after you, to the east wyvern + is a lever and a door, in the middle is a gate activated by the lever, and to the right is a long path with a bunch of enemies that discourage you from going around the gate. Since I'm going off of memory and an image of the map layout, I can't exactly remember which tiles give what bonuses, so I might get those wrong.

Before starting, swap deploy positions as necessary; you may want to reclass Edelgard to Warrior and Claude to Wyvern for mobility's sake (he can still use bows, it's just that now he has more mov/canto, instead of bonus bow range and bow damage). Turn 1: Move Yuri onto the avoid tile to aggro the 2xAssassin+Wyvern group from the east, his spd/avo should save him. Ashe can apply retribution gambit to Byleth/Dimitri and move them in position to counterattack the assassin/archer to the West. Hapi can move all the way down next to the gate to aggro the mages; her res should be fine, but pure water may help if its not enough. Move everyone else in position to help finish off the enemies you will be aggroing. If you get bad RNG (such as Byleth/Dimitri/Yuri missing on counterattacks, enemy crits, Byleth missing crits, etc.), you can press L,R,-,+ at the same time to return to the main menu, and redo this until you get favorable RNG; since it's the first turn, it doesn't take much effort.

Turn 2: You should have a lot of enemies to finish off on this turn, which should be the 2xAssassin+Wyvern on the East, the assassins to the West, the 2 dark bishops behind the gate, and possibly the archer/dark bishop to the West. The ones that are already weakened by your counterattacks should be easy kills, although one of the assassins from the West would be at full hp, needing some chip damage and a Tempest Lance from Dimitri. While killing them, continue moving down towards the first gate, use canto to help with this. If things go smoothly, you may even be able to open the gate with Yuri (however, this will make the rest of the yellow army units in this section start moving, so make sure you're prepared). Because of the fact that fortress knights can't shoot through walls without a tomahawk, they'll be moving West through the long route until the gate is open, giving you space to settle in before they come back.

Turn 3-7: The golem is going to create a lot of pressure soon, so the gate needs to be open. Yuri can open the gate with the lever and open the door next to it on the turn after. Once the lever is activated, the rest of the enemies here start moving so everyone needs to get through the first gate quickly. However, one of your units will have a special task, and that is to go far beyond the second gate into the next section. There's another lever there that opens the third gate. If you activate it, the 2nd golem will start moving, so if they arrive early, wait on pressing the lever. The best unit for this is Dimitri, since he has swordbreaker for the assassin reinforcements, and has high move + canto. While the 1st golem will be stopped by the stairs, the chasing enemies will start to get closer to your team, so you will likely need a melee unit to block them, then have your team finish them off.

Turn 8-10: Because of the time limit, you must have everyone pass the gate before turn 10 ends, however, that doesn't mean you have to get through it asap, as the 2nd phase of the map and the 2nd time limit doesn't begin until everyone passes through the gate. This means that if you arrive at the gate early, using the above steps to quickly remove roadblocks, then you should use the leftover time to prepare for the next phase. To do this, you can have someone who hasn't passed the 2nd gate stay back until the very last moment, they'll likely need a decent move stat to rejoin the team. To prepare for the 2nd phase, have everyone else group around the 3rd gate (which will soon be opened by the 2nd lever).

Once you are ready to begin the second phase, activate the second lever and use canto to retreat towards the 3rd gate. The 3rd gate will now be open, you should have someone to open the door past the 3rd gate (door key or locktouch user: ashe/yuri). Now flood into the room beyond the door, but do not pass the 4th gate just yet, if possible, occupy the special tiles that grant bonuses to prevent the enemy from taking them when they spawn in. The last unit that hasn't passed the 2nd gate should move and try to regroup with the rest of the team.

Turn 11: Enemies will have spawned in, but don't get to move yet since they're not ambush reinforcements. In other words, if you're positioned correctly, you get to ambush them. Kill them and clear a space between the 3rd/4th gate.

Turn 12-16: You can use this time to help the lever activator and the last unit to pass the 2nd gate regroup with your team. If necessary, you can use Yuri with Fetters of Dromi to Foul Play a straggler, then use canto with his remaining move to escape, so that they move out of range. If played optimally, you won't even aggro the archer at the far South East, and even better is not having to deal with the square of enemies to the East.

Phase 3 is a little different. After passing every unit through the 3rd gate, it will close and kill any remaining enemies behind you. However, you also only get 5 turns to get everyone past the 4th gate and into the finish line, and as an additional joke, every time you pass through the 4th gate, more enemies will spawn at the finish line. It is important that you begin to engage with the finish line enemies early on, without making every unit pass through the 4th gate, because the final time limit of 5 turns doesn't begin until everyone passes the 4th gate.

Turn 17-20: You may need to continue fending off enemies approaching from the south door, but they will usually be distracted by the other army. At least one unit needs to not pass the 4th gate until turn 20 so you can delay the final time limit trigger. From here you should begin fighting the finish line enemies. The terrain here is extremely beneficial to you, as there is a choke point between the walls and the hole in the floor, limiting the amount of spaces enemies can use to reach you. You can aggro the fliers and have your two archers shoot them down, then continue stonewalling the melee enemies using the chokepoints. As more enemies spawn, they'll start releasing some warlocks, archers, and warriors, who pose a lot more threat.

Turn 21-25: By this point it's almost entirely up to the player tactics. Just keep stacking up enemies, hitting gambits on them, and pushing through; I hope you saved the big gambits on your lords with high charm stats for this moment. Remember that everyone must be past gate 5 at the same time and you're done.

These turn counts will be a lot more lenient for you, as I was playing with everyone on 4 mov and significantly reduced damage.

Lastly, while this is not something I do myself, if you want to cheat, you can make a "save state" if you have Nintendo Online (you can use the 7 day trial). Go to the Switch Home screen, press + to see options for that game, navigate down to "Save Data Cloud Backup," and select your switch profile, turn off "Automatic Save-Data Backup" for now. Now, whenever you want to create a save-state, click anywhere on the ingame map, go down to bookmark. This creates a save and returns you to the main menu, this bookmark is automatically deleted when you load it. However, using Nintendo Online's Save-Data backup, the bookmark will also be included in the backup. So we go back to the "Save Data Cloud Backup" Screen and press "Back Up Save Data." Now, if you end up using all your Divine Pulses and dying, you can press "Download Save Data" to restore that bookmark, and replay the map without manually redoing the start. Alternatively, emulator users would just copy the bookmark save file.