It depends on the type of experience you want to have: the average tourist stops in Tokyo for 4-5 days and then leaves to discover Japan. I have always stopped for a long time, 2 weeks: the city is huge, there is always something different and new to do and see and, above all, in this way you can get in touch with the culture of the inhabitants of Tokyo and with their way of life. Tokyo alone deserves a trip and relegating her to a quick and temporary visit is, in my opinion, a real shame.