Its not so simple, first they have to prepare to move and prepare all their equipment to move, that already takes a few days. Moving the men is meaningless without moving their equipment and that part is not so simple as you think. Its very clear that you have no idea of the logistical effort involved.
We are not talking civilians here, we are talking combat troops with all their heavy equipment and supplies, can't do in 2 days, period![/quote
China army already station close to border with Vietnam, most of equipment can be move in the same way they move their troop, they move their millions army within China not away from China.