Is the shuttle running between the Doubletree hotel and the convention center 24 hours? It doesn't say in the description.
I don't believe Doubletree's shuttles are 24/7; only perhaps to the airport. I don't know what exactly what Doubletree's policy is though.
If it's anything like my hotel (Staybridge Suites, which is a block Doubletree), the policy is the shuttle runs from 7am-8pm by request 24 hrs in advance and within a 5 mile radius of the hotel. However, both hotels are about 5 miles away.
The Doubletree FanimeCon shuttle is available 24 hours, although in the late night hours, it will be mostly an on-call service. Still beats walking!