You have a ~10 minute window every ~90 minutes IIRC. The HAM sport is mostly about establishing contacts of increasing difficulty, not about making boring, roc

You have a ~10 minute window every ~90 minutes IIRC. The HAM sport is mostly about establishing contacts of increasing difficulty, not about making boring, rock-solid reliable communication links. 10 minutes is plenty for that, and helps stop people trying to hog the thing as only one person can be received at a time. Outside experimentation (e.g. trying an antenna, transmitter or receiver design), the HAM radios on the ISS are also used for school-astronaut contacts.