When does the "no-fault" six month period begin?

You do not have to be separated for six months before a case can be filed. The time requirement* has to do with how long you've been separated at the time your trial starts not when you file. Parties often start their cases by using another ground for divorce and then later convert their case to one of "no-fault" once enough time has passed.

* Parties can agree to use "no-fault" as their ground for divorce after a six month period of separation. If both don't agree to use this ground, then they must be separated for two years before a divorce can be granted on the grounds of "no-fault".