I board my two horses just because I work twelve hour shifts. That being said, I do clean my stalls and set up feed for the horses once a day, but it works out for me since the barn provides turn out, turn in, and does the actual feeding twice a day, as long as I set up hay and grain.
When I had to do complete self care and get to the barn twice a day, I found that there was not enough time for me to sleep on the days I worked.
If I worked ten hours or less, I know I could do all my own horse care.
Something to consider besides the length of your work day is how many hours a week you work, and what other responsibilities you have that take up your time. If you work around 40 hours and don't have a lot of other stuff going on, I'd think you'd have enough time for a horse.
Along with my 12 hour shifts, I have 4 days off a week. So even though I can't ride on the days I work, I still have 4 days available to spend exercising horses and doing care I don't have time for on days that I work. That's plenty of time off even to condition an endurance horse. When I worked 8 hour days, I found that I could fit in time to ride most days if I wanted to. It would probably be difficult to ride with a 10 hour day, but hopefully when you do those you have more days off in between.