Effectiveness of the pill?

I take my birth control pill everyday at mostly the same time. The only times that I sometimes don't is accordingly with my work and college schedules depending on what times I have to get up but I always take them within 2-3 hours of each other but mostly at the same time on the dot everyday. I just read through my whole birth control information and it doesn't say on there how many hours that I should take it within the hour that I normally do for it to still be 99% effective. Do any of you guys know?