Do I need a Eval license for V-center 5.1 trial?

Hi,

I am upgrading my Vcenter 4.x to 5.1 production setup. (and later ESXi when have license)

I have intsalled Single sign on and inventory services, and now trying to upgrade V-center

I dont have new license yet, If I upgrade now and dont add any license, will it continue to work for

another 30 -60 days?

Or Do I need to add any Eval license for the time being?

Thanks