The Leasing Broker and you as the co-broker (you are bringing the Tenant) must sign this agreement or include it in the LOI. It also depends if it is commercial or retail space, there is a difference.
Typically commission is paid 50% at lease execution and 50% at Tenant move-in.
It depends on what the L/A has put as the split.
Here, we have some that are "flat" fee's for the 12 month lease. No monies after that regardless of how long the initial lease is signed for.
I've seen some from $200 up to 5% for a 12 month lease. Really depends on what the owner wants to pay for the commission.