when to present bigs?

[nbosista]

I'm a founder of a new sorority and we're having our first official rush in the spring, I was wondering if it would be better to present bigs when the new rushes get pinned to pledge, or to wait till the end at initiation, or sometime in the middle? I can see doing it when they get pinned to pledge because they would need the support and help of their bigs, but I heard some other orgs don't do it for awhile...??? Any suggestions would help, so that i could bring it up at our next meeting!