Early morning alternative to fish market

Hi, I'm going to be in Tokyo for the 3rd and 4th May. I had plans to go to the Fish Market on the morning of the 4th but now I understand that it will be closed because of the public holiday. I want to sleep as little as possible as I only have 24 hours there - can anyone suggest an alternate early morning activity.

You could go to the Tokyo International forum, just to the northwest of Yurakucho Station. There is the Antique market there starting early, which is very interesting.

the antique market sounds very interesting. I check it only open on the first and third Sunday of each month from 8 to 3pm. Is there anything similar which opens more often?

Tokyo seems to have pretty limited offerings before 9 or 10 a.m.

Meiji Shrine is open at dawn, but other than Tsukiji it is the only major tourist attraction I know of myself.

So what else is there to do in Tokyo when one is wide awake at 5 a.m.?

There are a few 24-hour Don Quijote stores in Tokyo, which could provide some entertainment in a pinch, I suppose. (Which ones are biggest/best, can anyone kindly say?) Are there any big 100-yen shops open? Anything more interesting than the ubiquitous convenience stores?

Are there any other suggestions out there? Shrines, parks, stores, markets, urban art... ?

How about places that open at 8 a.m. instead of 9 or 10?