Isn’t there a requirement to take the ride within a specified amount of time after completion of the training course?
There is! The current ACP Manual requires that a flight check be completed within 30 days of the recommending flight training event.
If the flight check is delayed and will take place beyond the 30-day period, the chief pilot or their designate can sign and date a letter attesting that additional training was provided and the training was considered sufficient to ensure the candidates competency to complete the flight check. It's my experience that instead of going down this route, most companies will just have the pilot complete an additional training session where a new nomination is provided rather than having the chief pilot sign a letter.