Hi...
Here's an excerpt from the ATP Airplane PTS;
NOTE: The 24-month limitation does not apply if the applicant:
1. is employed as a flight crewmember by a certificate holder
under 14 CFR parts 121, 125, or 135 at the time of the
practical test and has satisfactorily accomplished that
operator’s approved—
a. Pilot in command aircraft qualification training program
that is appropriate to the certificate and rating sought;
and
b. Qualification training requirements appropriate to the
certificate and ratings sought; or
2. is employed as a flight crewmember in scheduled U.S.
military air transport operations at the time of the practical
test, and has accomplished the pilot in command aircraft
qualification training program that is appropriate to the
certificate and rating sought.
Regards