Time taken varies from application to application. Generally you will have a migrated application ready for testing within a very short space of time, less than a day. The migration of the data is the gating factor and is where most of the migration time is spent. As you would expect the time is determined by the quantity of data to be migrated.
However, during our extensive testing we were able to migrate 100Mb of data within 1 hour and 2.3 Gigabytes of data in hours – but each environment will have its own characteristics and requirements so these timings are indicative and may not be the same in your environment.