You'll know if it's going to get stuck, as stage 4 always gets stuck when it gets to the police. So it depends on how fast your police department is. The best thing to do is to wait four weeks after submitting the DBS check request. After four weeks and you still don't have your certificate, contact the DBS to request an explanation.
If the application has been in phase 5 for more than 10 days, the applicant can contact DBS to process it.