Its one of those GM things I think. At 20 hours a week with a job where that's split over shorter shifts 60-70% of the time your going to be able to work round it. Sometimes however your going to need to say "I can't make that because I have to pick the kids up in the morning" and sometimes the GM's going to say "You have a commitment this week for X and you've been offered a run for X." so you need to figure out how to deal with it. What happens then is up to you and the choices you make. Maybe you pass on the run, maybe you call in sick for work, maybe your sweating and watching the clock the whole time your meeting the johnson making him suspcious when really the reason is you know if you don't leave in 5 minutes your going to be docked a day's pay because you wont be at work on time and for a part time driver they take the view be here at 6 to pick up the bus or we get someone else for the day.
There are way's to work round it if your not awakened or willing to take the hit you can get the sleep regulator so you only sleep 3 hours a day meaning you can be doing run work till 2-3 in the morning regularly assuming you start your day at 6. Researching information, hitting a facility, meeting your contacts etc, etc. However as Darzil said it is a negative quality and as such it is going to have a negative effect on you so there will be times you have to choose between the two. The higher the quality the more the effect whether its a 25 karma corporate SIN where they know exactly what your doing and are just waiting till you either hit a corp faciltiy you shouldn't (not even necessarily the one you have as your SIN but one of their sub, sub, sub, sub, sub, sub, sub, contractors who were offlimits) when they slap you down hard or they have use for the new skills you've aquired since you are still a corporate employee regardless of what you choose to believe (or if you took prototype transhuman corporate property) or a 2 point superhuman psychosis where you might care for the normals that belong to you but never make the mistake of thinking they're as good as you.