The seconds in a moment is just a brief period of time. Therefore, it all depends on what's going on in the moment. If your mother is on the phone and you ask her a question, when she replies with "Wait a moment", that moment could be a few minutes, or maybe until she gets off the phone. I would think that a moment would be based more on minutes, then it would be seconds. If it was based on seconds, then your mom would have said "Wait a second", right?