One daughter is in third grade the other in kindergarten and my son is only 3. Im at school all from eight am to nine pm on wednesdays and mondays and im there four about four hours on tuesdays and thursdays. The kids sleep at my house in their room. I "parent" them when i get home from school and on my days off friday thru sunday.
So during your weeks, realistically speaking, you don't see your kids on Monday or Wednesday. I'm going to assume you're in school for 4 hours during the same times your older kids are in school on Tuesday and Thursday, and you're with them "full time" on Friday, Saturday and Sunday.
Do you have a job?
Wouldn't agreeing with Mom on a schedule that allowed you more actual time with the kids, even if fewer overnights be better for everyone?
Perhaps Tuesday evening until 30 minutes or so before bed time, and then Thursday/Friday every week and alternate Saturday/Sunday with Mom. Mom would then have Monday, Tuesday and Wednesday nights, with alternate Sat/Sun.
Yes, out of a 14 day period, you would only have the kids for 6 overnights instead of 7, but you're only seeing them for 5 now, considering your schedule.
I think it's unlikely, if this goes to court, that a judge is going to award you 2 days every week that you're not home from early in the morning til after bed time.