Checkmate waits for your Mac to become idle, and then begins testing. Some of the tests run at most once per day, others will run at most once per week. The tests that run weekly are those that represent additional wear on a drive, such as the volume structures and surface scan tests. 

The surface scan test stores the current scan progress if it is unable to complete testing on a drive, and will start testing from that point during the next testing period. Once the test has completed, Checkmate will wait seven days before beginning the surface scan test on that drive again. Likewise, the volume structures test will wait a week between completed tests.