Like January, February is a good time for visiting Japan as the weather is usually sunny and dry and sightseeing spots are not crowded. The downside of a visit in winter are the relatively short days (sunset is around 5:30pm in Tokyo) and the vegetation's barren state.
1 A healthy person drinking approximately 2 liters of water per day makes 800 to 2000 ml of urine per 24 hours (4).  If the urinary system is healthy, the bladder can hold up to 16 ounces (2 cups) of urine comfortably for 2 to 5 hours (5).
It takes 30 to 40 minutes for food to digest in your stomach and 3 to 4 hours for it to absorb in your intestines. I agree that there is no strict formula for this, since it also depends on what you eat and how you intend to expend that energy.