Why is 7-11 called 7-11?

I have been wondering why it is called 7-11.

When the first one opened, it was the hours it was open.

Really? i wonder why they didnt change it?

Way OT, but a funny story that the topic reminded me of...
The local Denny's Restaurant a few years back decided to give it's employees Thanksgiving Day off. The funny thing about it was, they couldn't find the keys to lock the doors. It seems as though, being an establishment open 24hrs a day 365 days a year, never had to lock the doors since being built. So they had to get a locksmith to change the locks on the doors. The 7-11 hours of operation kind of got me to remembering this story.