I asked the store clerk and was told the hours are 5:00 A.M. to 11:00 P.M. (as opposed to 24 hours as it says online). Can this be confirmed?

I can confirm from personal experience that they close at 11 pm. I'm curious whether the 24 hour thing is a misleading bug. If some Arco stores open 24 hours and some do not, I would advise Arco/Google Maps to make sure their information is accurate per location, not just issue a blanket statement where all opening times are the same.

There are several like that. Just go to the one in Livermore.