Well, you got me, I'm afraid. The only thing that comes to mind is a form of eczema called dyshidrosis, which produces little bubbles or blisters an the fingers or palms. Whether that's what these are, or why they appear in the afternoons and beyond, I really can't say.
I will say this: your symptoms don't remind me of anything significant, and often, inscrutable stuff like this just comes, hangs around for a while, and disappears without a trace. I'd just keep the skin moiturized with any lotion you like, and wait for it to either disappear or show some other symptoms (which I frankly doubt will happen.
Best.
Dr. Rockoff