This varies from state to state. DirecTVs actual policy I believe is that as soon as the tech activates the receivers you are on the hook for however long the equipment lease is (18 months for SD receivers, 24 months for SD DVRs or any HD equipment I believe).
DirecTV's policy is overrided by state consumer protection laws though. So if your state says you have 24 hours then DirecTV has to give you 24 hours, if you state gives you 14 days then DirecTV has to give you 14 days, etc.
So to answer this question you really would need to look into your own state's laws. I'm not aware of a site/thread that lists them so it's easy to find out. Maybe that wouldn't be a bad idea for a sticky thread somewhere around here if someone wanted to put together a list and keep it updated?