The moment of placing spawners is part of a strategy a faction can choose to follow. The shorter the time befor payout, the more people they need to be able to get online to actually be able to place the spawners. The more obvious it is that they are doing so. It is an advantage and a giveaway. If they cannot get enough people online, because of sickness, school, work, bad internet or other reasons, they are at risk. Those risks are not involved when a faction choses to plaece their spawners more time in advance.
Spanwer placement timing is an important part of faction playing strategy, always has been. It would be a great infringement on the game dynamics if factions were not free to chose their own moment.