Originally Posted by
Finkface
But the bolded part is independent of (“in addition to”) the check in time limits and there is no exception stated for connecting tickets vs originating flights. It is a stand alone requirement. You are required to be at the gate by T-15.
“Additionally, you are required to be at the gate and ready to board at least 15 minutes before your scheduled departure time. “
It actually depends on the flight. Most domestics are T-15, but some shuttle flights are as close as T-5.
Also, for most international flights on DL it's T-20.