Should I set up my integration tests as a continuous build or a night build?

In my project, we have a set of tests for integration, which are usually slow compared to unit test devices. Typically, it takes about 3 hours to complete the integration test run.

My question is, should I configure my integration test test as a continuous assembly (which, obviously, depends on my continuous assembly of unit test fixtures and works after that), or should I configure it as a night assembly?

If I configure it as a nightly build, will it expand my feedback loop?

Thanks, -Mike