One thing to add to the above. The Keisei "platform" at Ueno is not in the huge JR Ueno Station. It is actually in the Keisei-Ueno Station, which is a separate facility kitty-corner across the street from Ueno Station, near the entrance to Ueno Park. There is an underground passage between the two or you can exit JR Ueno and walk over on the sidewalk.
Oh, and I agree with both above. You may be trying to cram too much into 24 hours.