Plumbing problems can happen at the most inconvenient times of the day or night. Sometimes, they happen during those times when you need to use them the most, like when you need to take a shower before heading to work, but then there is no hot water coming out of the shower. Maybe when you really need to use the toilet, but then you find out that it is clogged or will not flush at all.
Nights, weekends, holidays, whatever time of the day, or whatever day of the week, such instances do happen, and when they do, you can count on Mr. Rooter to be there to help you out.