Why not? They kicked off the Hero on Saturday, October 11th (or was it Sunday, October 12th?), but allowed Best Buy to distribute the pre-ordered phones starting on Friday.
IMHO, Sunday is the worst day you could possibly kick off a highly-anticipated phone... tech support is at its weekly skeleton low, customers with problems that can't be resolved until Monday are furious, and users for whom it works fine are frustrated that they only get to play with it for less than a day before having to go back to work on Monday.
Personally, I think Friday launches are ideal... it's a weekday, so no problem is likely to be truly insurmountable "until next week", but it's right before the weekend. The uber-hardcore buyers can take Friday off just to be safe and enjoy three days of celebration before going back to work on Monday and showing off their new toy. The less-desperate early adopters can buy it at lunchtime, and the remaining users who stream in over the weekend are less likely to go postal and freak out if some "only-in-SprintLand" provisioning/account problem crops up that can't be resolved until Monday than the group that takes Friday off from work to camp out on the sidewalk and make sure no employee gets out of the store -- dead or alive -- until their new phone is safely in their hands.
