Times are definitely longer and finds smaller for smaller bodies. My impression is that below about .1 gravities, the wait is so long and the reward so small there is no point in a survey.
The few times I have tried to use a geo team on an asteroid it has taken much longer than normal to get a result, and it generally doesn't get much of a result compared to a planet even then. If you are trying to get the teams rating up then the better option is to use a gas giant moon as it will be much faster than the asteroids seem to be.