CPEs have to be earned within your certification cycle dates. Your cycle will start the first day of the month following your endorsement application being approved.
e.g. If your endorsement is approved today your cycle start date will be 1st October and that will be the earliest date when you can start earning CPEs.
You can read all about the CPE requirements in the CPE Handbook:
I am curious to know if CPE credits earned after the exam and during the endorsement process can be counted towards the first year?
all CPE must be earned after you are certified.