i have been trying to 100% stuff for the squirrels vs skrulls event and it takes too much time that i dont have
You're probably going to need to be more specific to get any useful advice. There's lots of sources for the acorns: the Objectives, the Acornucopia side quest, the normal monthly quest, and arena events. Altogether they can take a substantial amount of time, but as with every part of the game if you can't do everything, just do what you can. At the end of the day, you have to be able to accept your limitations and just try to do the best you can within them. Think about what time you do have, and then try to focus on the things that will return the best result for that time.
I am able to 100% every difficulty every month without using refills. My strategy is when I don’t have much time, go into chapter 3 of weak content with my strongest champ. Wreck the fights and use all my energy in 5ish minutes. Easy to do on a bathroom break. If I have more time, I will do chapter 1 or 2 and use weak champs for fun.
Also, I sometimes auto fight while working on other things. Like while I’m cooking dinner I’ll just reach over every so often and go to the next fight and let the AI do it.
chapter 3 is annoying because the energy cost of each tile
That's just how the monthly quest is structured, the energy costs rise with each chapter. I don't know how much energy this month takes, but the Heroic monthly map has been running around 1300-1400 energy for full completion. It seems like a lot and I don't know what level you are (the higher your level the more energy you have at the energy cap) but if you can burn about 50 energy in the morning and 50 energy in the evening doing that map, you'd be done in two weeks. And that's not a huge energy burn. The side quest takes zero energy, so there's no other demands on your quest energy this month.
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Also, I sometimes auto fight while working on other things. Like while I’m cooking dinner I’ll just reach over every so often and go to the next fight and let the AI do it.