Define “taking too long”.
WPT tests go into a priority queue and the tests are run in the order they are submitted (with API tests getting a lower priority than interactive users). If you are submitting tests to a busy location it could take hours before the test is run. Even if you are submitting to a less-busy location it will usually still take several minutes to get a result.
If you want control over the test times and need test results faster (or with guarantees) you need to run a private instance where you have full control over the capacity and testing.