Salesforce Certification Retake Policy

We can attempt Salesforce Certification 3 times in a particular release. Every year, we have 3 release cycles from Salesforce. So, we can attempt 9 times per year.

To know about releases, check the following link
Salesforce resets the retake count end of every release. 
For the 1st retake(after 1st attempt), we have to wait for 1 day(24 hours) to register.
For the 2nd retake, we have to wait for 14 days. 
For the 3rd retake, we have to wait for the next release as you have surpassed the 3 attempts already.

Reference Article: