There isn't a set time, per se, but once you pick a time that you think will work best for you, you need to stick with it. I do mine between Fridays 7-8 pm and it works out pretty well. There was an interesting thread on this very subject that another forum member was also trying to find...people listed their shot dates/times and when, if at all, sx popped up. It was an interesting read and ALOT of variations.
Just as "justme53" said, there is no set time and, if necessary, you can change that day and time. I used to do it on Tuesdays, between 6-7, depending on when I finished dinner. I always do it on a full tummy. Because of a change in my work schedule and that I always want to do the injuection the evening prior to my days off, this week I did it on Monday at 7, and next week I will do it on Sunday, which will be my permanent day. Having Monday and Tuesdays off now, if I have any side effects from the injection I won't have to worry about missing work.
Good luck
Most do the shots on Friday evenings,i did anyway from between 6 and 9 pm,i just relaxed all weekend and by Monday i was ready to roll