SpecFlow - Integration testing (messaging architecture + scheduling issues)

We are currently using SpecFlow to do some integration testing. This is somewhat challenging when using a messaging architecture and time based tests.

For the messaging architecture we currently do the flowing: 1) API call is made. 2) SpecFlow checks the queues every x time until it's empty before proceeding. 3) Empty queues = processing is done so that means assertions are left.

For time based tests we currently don't have an good idea on how to implement this. For instance, we sometimes schedule a message in the future. When it comes back it produces a result. What we do now is make sure the scheduling time is limited to let's say one minute based on the input and then wait a minute before asserting. This works, but as more and more tests are written and SpecFlow needs to wait more and more, the tests become slower which I don't want.

How do others tackle these issues?