Should I keep my lemon bars refrigerated?

I’m making lemon bars for my father and taking them to the nursing home where he’ll be with my mom. The drive to the nursing home is 1½ hours from my house. How long can the bars sit before they need refrigeration? I’ll probably bake them tonight and I’m visiting tomorrow, late morning, but it’s possible I might make them in the morning before I leave.

The recipe is similar to this one.