Do you NEED to? I'm sure plenty of folks get along alright without having a set schedule. They certainly don't go out and catch a rat every Tuesday at 7pm in the wild.
However...feeding on the same day of the week every week has many advanatages, especially if you have multiple animals to care for. For the last couple of months, my feeding schedules have been in a bit of a flux, because my life has been in a flux...and the snakes are doing fine and eating well anyhow. But I miss my regular schedule and plan to get strict about it again as soon as I can.