I think one and two weeks is to short, 3 or 4 weeks is fine to give admin team more time get cheates out
people shall not buy worthless players so also that get be better
other thing i think all players get more worthy because you have more secure.
I think a full month will give people a good idea if the potential soldier/assisstant will be worth bidding on. A new player may be active the 1st week and then give up my the end of the month