Carter states at the end of the episode that there is no way to know how much time passed. Actually, this isn't true, they can know the time. Very few planets were in the timeloop with them. They can go anywhere they were before the day the timeloop started. If there passed more than one day, that planet wasn't in the timeloop, so the time passed regularly there, and they can calculate the real time on Earth. Even more simple to ask their own teams, who were out somewhere else during the events (and couldn't come home).