Timing issue

So tomorrow I have plans for a ritual to Mercury. The book states it has to be done on the day and hour of mercury. It looks like the best times for Wednesday to do this are 7:00 am, 7:00 pm, and 3:00 am. I typically do rituals only at night. However I have a class at 7 every Wednesday. Will I still be successful if I did it some other hour or day, or do I wait till 3?