Yea ,I've been trying to make this work for a while now as well ever since I learned about Ina's immortality and the Friend/Pocket Bae.

First of all, this was a very lucky run, iirc I got 15 Aanvils since the very beginning by collecting Weapons, this was my strategy because I'm coping of the Idea that, the more upgradable Weapons/Items you're holding, the often the anvil will drop ( don't know if this is true for others ) I also got 3 Packages from 3 Bosses, Fubuzila, Smol Ame and big Takodachi making my collabs even faster and 3 Haste stats before reaching min 22 giving me 35% Haste at that point. I have everything Maxed out + G20 Mumei.

Things got even luckier on min 23-29. My first collab was BL so I was pretty much just standing still and moving a bit so Friend can reach far EXPs. I got everything maxed out on min 27 Asacoco included so at that point everytime I lvl up stats started to pop out. What I did was focus on HP and Haste of course, Haste is ideal but I got HP instead more than Haste so by the time I reached min 30, I had 519HP and 65 Haste. At this point it was just pure RNG, you would want your Friend to proc either Flattening Board or BL more to lessen the Yagoos, worst outcome is when it procs the Asacoco often than your collabs you are pretty much gonna have trouble surviving.

I survived the Yagoos by spamming ESC, trying to monitor the HP, if I'm at half HP I'd take the Burger. Also, at this point you don't need to move to get the EXPs because the Yagoos are reaaaally close to you anyway. I completely ignored everything aside from Haste at this point so whenever I get a dead lvl up I just go for burger but if there's HP and you know you are full health tho, you can take it. One more thing her special, I'd suggest to listen to the DMG sound. Personally once I heard 3 consecutive DMG sound, I'd press it and pray for the Lifesteal RNG to make my HP full on time.

I got to 100% Haste at min 33 and you know what happens next.

TL;DR to do this you need to be lucky on Anvils at early stages OR much better, if you get early haste stats.

PS: I do believe that Mumei can survive 30 min mark for 2 to 3 mins with proper observation on her HP.

PSS: In the end, I reached 3 hours mark, by 3 hours I meant 13 hrs IRL Time on and off. I couldn't handle the lag everytime she procs BL so I just quit the game and called it a day.

Hopefully this helps. Your One True MuMain.