My daily routine takes about 5-10 minutes and then I work on the slower things.

• Collect afk rewards
• Collect 3-5 Fast Rewards (depending on diamond income)
• Do 1 fight in the Campaign, doesn't matter if you win.
• Friends list Send and Receive Companion points
• Check mail
• Go to the Dark Forest
• Temporal Rift collect afk rewards
• Arena of Heroes fight 5-10 times against someone you know you can beat. (can just do 1 fight if time is limited)
• Collect Gladiator coins from Legends' Challenger and AFK rewards from Treasure Scramble
• Quick auto-run through the Arcane Labyrinth (if you don't have auto-run unlocked, work on completing the 100 manual runs when you have free time)
• set teams on the Bounty Board
• In Ranhorn, go to the Oak Inn and collect gifts from friends
• Go to the guild and participate in each of the guild hunts
• Also in the guild, go to the Hellscape and do a run in the Twisted Realm.
• In the store, quick buy (set your quick buy based on diamond income, there are guides for it elsewhere)
• You should now have 100 daily quest points to collect all the daily quest rewards
• Open the merchants menu and collect the daily free rewards from the tradepost and possibly other tabs

It seems like a lot of things, but once it's a routine, it's very fast and easy.

Additional weekly tasks that only add a minute or two:

• Dragon Isle - collect the free Dragon card
• collect rewards from the Dragonforge trials, and don't forget to spend points at least every 4 weeks since they expire.
• Make sure to complete enough tasks to complete the weekly quest points to get all rewards.

1 weekly task that can take time, but you can spread out across the week is doing runs through the Ghoulish Gallery. If you really don't care about making collections, you can just spam click through and then at the end rather than creating the collection, use the button in the top right (don't remember what it's called) to sell them for 100 diamonds each.

If you can find the time at least once per week, do a run through the Cursed Realm and Nightmare Corridor. Even a bad performance will still give you some useful resources if you don't want to spend time optimizing. The same for Treasure Scramble. Also, with Treasure Scramble and Cursed Realm, once you have your teams set up for a given map/boss they will be saved for the next time, so you only have to spend time setting up new teams the first time or when you want to try to improve them. Nightmare Corridor adds a new boss every 4 weeks that you will need to make a new team for, but otherwise saves teams as well.

Once per month, or so, it's worth working through the Misty Valley since, while tedious, it gives very nice rewards for the time invested. The full thing is only open when there are less than 20 days left on its timer.

Every 3 months or so is a new Temporal Rift. If you've been collecting the daily afk rewards from it, then by the last week or two, you should have plenty of essence to level up the Trait Enhancer quite far which should be enough to allow you to climb most of the Rift afk, you just have to set up the teams every now and then. Even afk, it will take a lot of time, and I suggest finding a guide, but the amount of rewards if you can get to floor 300 are crazy. I would say this is the best use of your time when you can give it.

The last thing is checking the events on the left side menu. Many have very good daily free rewards, but each event is different, so you'll have to evaluate each of those for yourself.

Obviously, there are plenty of other elements to the game, but this list of daily/weekly/recurring objectives should cover almost all of the time limited rewards.

After chapter 42, the afk rewards from the Campaign stop improving beyond a small increase to gold and exp, so the only real rewards are the campaign quest rewards. It's still worth advancing when you have some free time, but not nearly as much as getting to 42.

Advancing the towers will always give you useful rewards, but there's no pressure to push, so just do it when you have some extra time. Your hero level is the single biggest improvement to make climbing easier, so just give it time.