Chelsea know United would sell for around £30million and are considering improving their £22m bid.
At a press conference in Indonesia, the final leg of their tour of Asia, Mourinho said: "It depends on the philosophy of each one. The sooner you have the players the better. You know the squad you have, you know what you have to work with, you have time.
"But, yes, he [Moyes] is right. Many clubs are waiting to the last moment to make their decisions, and those decisions affect a number of other clubs. The one who sells has to go and buy, then they have to buy to replace, so no club is safe.
"Until the last minute, a club can go and 'steal' a player. I don't mean steal a player, but steal the balance that a manager has when he's working with a team. We are okay because we don't have players to sell."