Flight problems??

Our son is teaching in Bejiing & is marrying his girlfriend there in May. We plan to come & know nothing about all this paperwork! Starting to freak. Ahhhh. Anyway, I've been reading and it appears we must supply the exact date of entry/plane ticket info. Dad works for a major airline, therefore we travel very cheaply, however, since we must fly on seat availability, we cannot state the exact date, nor do we actually "get a ticket" until right before we board a plane! HR has told him we will most likely have no worries with getting there/home. Does anyone know how big a problem this actually is??