Ok, look, it is doable. As worry said, really the only change in your circus is that one day of after school where you were anticipating dh to be able to do the collection whilst you are at college.
3x childcare for one night of after school is an expense, but there might be a cheaper option. Have they all got friends that you could arrange a weekly standing play date? And for you to reciprocate on a non-uni day? (from what you have said it looks as though you are only there two afternoons past school pick up?). Make sure to check out after school clubs etc as well, sometimes it works out better.
I do sympathise, have been in exactly the same boat (3 kids, studying, dh working long hours or away) and made do with an interesting and convoluted mish mash of different childminders, after school clubs, begging for help etc. it ain't easy, but it is of course more than possible. It depends how much you want it, and how much you want to play the victim.
(I didn't really mean that, but it is aibu. Quite why you posted it here is anyone's guess, but sure, have a moan if it makes you feel better)
Don't underestimate the workload of studying with 3 kids, by the way. I would turn up for college having done 3 school runs to 3 different settings (having painted one kid purple for book day or whatever), popped to the hospital to drop off some paperwork and collect some meds that had to be refrigerated, rushed home to get them in the fridge, then driven the 45 minutes to uni to get into lectures before 9.30, only to find a room half full of hungover teenagers moaning about the essay due in at the end of the week, with a handful more wandering in as the day progressed. Then dashing out at 5.30 to go and do two or three more pick ups from after school clubs or childminders, depending on what day it was, whilst they all drifted back to the bar.
Go on, lady. You can work it out. Don't be such a pessimist. You are talking about one day a week where your plans have changed for about 2 hours.