Witht eh current cheap fares to SGN, I'm thinmking of using that as a base to get to Angkor and PHN. Assuming no more time in SGN than necessary- the inbound flight arrives around 11 at night, and the outbound leaves around midnight, would 7 nights "on the ground" be enough to travel to both places, and not feel TOO rushed?

Also, I know the Vietnam visa on arrival can only be gotten at an airport. Once recieved, does such a multi-entry visa allow re-entry through a land border?