This relates to the situation that one of my friends is in:

He has a visa to visit Vietnam, but the dates are wrong and he will be arriving in the country at 10pm the night before his visa is valid. He is willing to just wait around until midnight before going through immigration. The question is will the airline let him even get on the plane?

He is going to get this issue resolved before leaving in over a month just to be safe, but it would have been terrible if he hadn't noticed until just before.