If the ISS orbits say 16 times a day, averaging 90 minutes, it only crosses the Greenwich Meridian (0° longitude) 15 times in a day, or averaging 96 minutes.
A kid asked me how often it comes over a day. Which is the right answer? He was presumably meaning coming over our country.
(Sometimes we can see consecutive passes, but of course you can't take timings from them, it depends when it is in sunlight.)