It's a stupid idea. Most folks do it on the flip side of their first fleet tour at their B-billet.
That said, I did it. I waited 7 months for IFS, so I took 6 credits while in IFS/A-Pool, on top of my stash job. Two extensions later, it spilled over into IFS and API, and I got away with it (i.e. without detriment on my performance - I've been using TA so my chain of command's signed off on it). Not knowing what to expect, I put it on hold for Primary, and ended up pretty bored and unhappy. Not any the wiser, and expecting a three month stash for Advanced, I signed up for another three credits in Advanced pool......and ended up working on the class through most of Advanced.
If you really want to do this, know what your priorities are. Before I started I promised myself I'd never let my self-inflicted extracurriculars detract from flight school, because I have no intention of explaining that I got a pink sheet because I was busy studying XYZ. Flight school's come first, and I've been ready to drop the class like a rock if it ever threatened to get in the way.
When my stash job (at LEAD) went from PT Marines, teach a class, go to the beach and drink beer, to a 0600-1700 gig, I upheld my responsibilities, let my homework deadlines slip, pleaded for an extension, and my professors were understanding. Same in Advanced when RI's came around and I didn't have time for anything but sims, INAV problems, and sleep. I can drop the class or get an extension - I did the latter and pondered the former. I haven't yet finished a class without extensions but the school I'm attending has a large military student body and the profs (many retired military) have been pretty understanding.
I justify it because I'm a dork and I'd be doing the reading anyway; the class helps me focus and makes me think and write about the same material, and I honestly enjoy it, so it's a net positive for my psyche. Don't attempt it if it'll just be another stressor. I also don't know how the engineering classes would work, and suspect they'd be harder and less flexible than my history classes. I just read 2-4 hours a week, got online and argued (erm, discussed politely) with my classmates (I think I spent less time on there than AW, to be honest), and wrote 500 or 1000 words for an assignment here and there. Somewhere in 4 months I found the time to research and write 3000 words. Honestly, I don't think I could have handled much more than that.