The station "receiving the delivery" drops in demand and recovers:
one primary station and one secondary station
if deliver to primary station ->
5 demand initially Jan 2029
drops to 4 demand one month later Feb 2029
2 demand after 6 pax car delivery in Mar 2029
Recuperates to 4 in Apr 2031
Recuperates to 5 in Dec 2031
if deliver to secondary station ->
4 demand initially Jan 2029 (starts at a lower demand)
stays at 4 demand one month later Feb 2029
2 demand after 6 pax car delivery in Mar 2029
Recuperates to 4 in Apr 2031 (I didn't catch the exact month)
Recuperates to 5 in Dec 2031 (I didn't catch the exact month)
Both stations operate the same as far as I could tell. There was no noticeable difference between demand dropping in the primary and secondary stations. Am I answering your question?
caveat: (it's possible if it's covering a city of 7, one station might slightly faster recover because the game might split the houses to be 4 at the primary station and 3 at the secondary, but I don't have motivation to be that precise).