It probably doesn't matter too much so long as it doesn't take you an eon to complete the degree. However, you do want to be able to demonstrate to the adcoms that you can handle the demanding courseload at medical school--This is your top priority. You should probably try to be a full time student if at all possible It's not easy to do work and school full time, but it can be done, but if something's gotta give, make sure that it's your work schedule.
I would not worry too much about how adcoms will view it, a lot of people have to work during college and they will understand if it takes you an extra semester or two to finish. The most important thing is to maintain good grades, that is the first thing the adcom will look at!