Originally Posted by
FlyerBeek
Not necessarily. There's no regulation that prohibits this provided a minimum number of FAs are onboard. In some cases, it can be a good decision to board without the pilots if the pilots are getting close to timing out or are called in from reserve with an unknown time of arrival to the airport. That being said, if they knew it would be a 90 minute wait ahead of time then it's probably not a great decision by the GA.
-FlyerBeek
I must just be an outlier then as I’ve had more times than I care to remember when the gate agent would hold back boarding until all crew members arrived.