decent pictures - can you get anything bigger though? It definitely looks very Prunus-ish to me. Does it release gummy sap? That would be another indicator that it's probably Prunus, I think. I'm no expert, but I've seen my share of cherry and peach trees. I think the exact species shouldn't make much of a difference regarding when to repot, but I'll let others with more experience chime in on this one. In the meantime, here's some good information regarding general care of bonsai trees of the Prunus genus:
http://bonsai4me.com/SpeciesGuide/Prunus.html . Repotting information is third in the list.