How is revenue moved from Unearned Revenue to Earned Revenue?

Hello,

I am working on a Project Billing implementation. We have been using Project Costing for awhile and I'm very familiar with how that side works, but Billing is new for me. I've gotten a good handle on most of the transactions and processes but I'm still struggling with the Unearned Revenue piece.

My question is how/when are journal entries created to move unearned revenue to an earned revenue account? For example if we bill a customer for 25% of the implementation price when the contract is signed, that revenue is not yet earned. So in Projects we would create a billing event that would generate an invoice to DR Accounts Receivable, and CR Unearned Revenue.