What if the tenants of an apartment sign the lease a week before the co-signer does?

Question

What if the tenants of an apartment sign the lease a week before the co-signer does?

Answer

Then the landlord has to decide whether to make the lease binding as soon as the tenants sign, or make it not take effect until everyone signs. Unless a contract says it must be signed at or by a certain time, when it is signed is irrelevant except it is only binding on people who have signed it.