When I was 22 or so and first got my green-card, I was going to school full-time for my associates and working full-time while slowly building-up my own small business. I was lucky to have a boss who worked around my schedule. Now even then i was doing 100+ hour of work every week with school included and barely sleeping at night with literally zero personal life. I took lots of online classes where ever I could, though that having had been 2002 there were not all that many in that format.
Got my Associates in science in culinary arts in two years(though could have done it in a year and a half.) A year after that I had built the catering and personal chef service to a point I could support myself by that alone.. a year after that expanded it to include a small hole in the wall restaurant.
How did I do it? Well was young with energy to spare, committed to my career-path and wanting to "make something of myself" to the point one could call it a type of insanity. (Basically burning the candle at both ends to make sure things worked right)
After 7 years of that and the economy tanking I joined the army for better career prospectives and a less stressful workplace atmosphere. (Not kidding about the less stressful bit, better benefits and pay too..)
Savings wise, even when working and going to school I managed to put away $100 or so a month. Which is not much, but on a break even budget when young its better than nothing. Also, I kept any cash tips as a backup just in case. Which was around $1500 a year of extra income.(were included in my taxes though.)
Now, I'm out of the Army.. retired due to disabilities incurred in service. Pushed through my bachelors in the span of 3 semesters and a summer term 28 units on average per term. Got my MS in just about the same amount of time and still have just enough GI bill benefits left for a 2nd MS which I'm looking at getting in to programs now... What you can do is all about dedication and drive, however being lucky with various circumstances can also be a very big thing.
If your employer refuses to accommodate time off for school it is probably a good idea to look for a new place to work at.