I also think the time between Michael saying goodbye to Alice ("i'll see you in a month") would mean between MC in jail and talking to Valravn the first time would be roughly a month... Michael was preparing for that fight to get his powers...
But time in the game isn't always clearly mentioned.
From what I understand the timeline from Jake's fight is like this:
-On day 61 right after finishing the battle with Jake Michael goes to prepare for a month after he says: "I'm going to go check on Mia and then I'm heading out. I'll see you in a month or so." to Alice.
-Then right after that is the Deryl fight and then there is a 2 months timelapse, after which, still being in day61's script Ella says: "Found it. At long last...." "After two long months in this damned cavern....", and then talks to monster Deryl and shit.
-This is further backed up when in day62 MC mentions that 2 month have passed since Deryl turned into a monster: "It's been about two months since my battle with Jake and Deryl.", And then there's the other Deryl... The one I've been hanging out with these past two months.".
-On day62 while at the mall he also make plans to come back to the mall with everyone next week when talking with Deryl and Amber: Deryl "The boys, back together, next week. You coming?", MC "Oh, sure. Let's do it.", Amber "Just wait til next week, we'll get to it.".
-They end up going to the mall on day76 (Yeah, I know that's technically two weeks, but on day69 MC just goes to visit Mia and there's no mention about the plans, so I take it that story wise only 1 week passed). That same day, but on day77's script, MC is ambushed by the police at the mall at the same time that Michael fights the lighting monster.
-We get to Deryl's house after fleeing, take shelter there and go to sleep.
-Then on day78 we get invited to talk with the supreme minister: "It is a meeting in good faith, to discuss our future. Which is why five days from now I will be flying out personally to Sector 1, to Prime Minister Miliken's estate, where I and he would like to invite you [hname], to a meeting."
-On day83 we go to a party and after the party we atempt to go to the meeting, but on day84's script we get teleported by Nico to H.E.R.O's base. After talking with Dexter and Xanthe for a while we are sent to fight Valravn and after beating him we go to bed.
-Next day we talk with Xanthe some more, talk with our friends, etc. And go to sleep after that.
-Next day we go to class, talk to some people some more, go to sleep.
-Next day Practice fight against Laurie, then memory scan, then sleep.
-Next day more classes, sleep.
-Next day more classes, tour of the base, talk with Xanthe, sleep.
-Next day a class with Xanthe, sleep.
-Finally on day91 we go to the interview, on day92 the fight vs Cole and friends, then there's the meeting with the captains and then we finally go to sleep again.
-Next day even more classes and even more sleep.
-On day94 we fight with Tiffany, and she invites us to her weeding that's gonna happen in "a few days", then Del leaves on his mission and we go to sleep again.
-Next day more classes more sleep.
-On day96 Xanthe feeds us spiders and then we go to sleep.
-Then on day97 we go to the weeding.
-Next (on day98) we talk to Xanthe and after that scene is the 1 month time skip and the start of the assault.
TL;DR:
*2 months since beating Deryl (With Michael going to prepare for 1 of those months).
*1 week until the mall.
*5 days until we get to H.E.R.O's base and beat Valvarn in the same day.
*12 days at H.E.R.O's HQ (Assuming there weren't any non mentioned mini time lapses, like 2-3 days skipped)
*1 month of training until the assault.
