Normally, it´s a bad idea to wait for all players to post. If you do so, you´ll have often to wait for a week or two when a player abandons the game, have any problem, or forgets to post. In that case, the other players may think the game is dead, the DM doesn´t care much, or lose themselves interest (it´s hard to follow a game when you don´t remember what happened the last post, or you have to check the rogue´s gallery to remember what character you are playing)
It´s much better to wait a reasonable, previously fixed amount of time (like 2-3 days if you intend to post 2-3 times a week, or daily for a faster game, etc) and NPC characters whose player hasn´t posted.