Man pages matching name allegro_usecs_to_secs in section 3alleg5:

ALLEGRO_USECS_TO_SECS.3alleg5.en	debian 10 / allegro5-doc
ALLEGRO_USECS_TO_SECS.3alleg5.en	debian 11 / allegro5-doc
ALLEGRO_USECS_TO_SECS.3alleg5.en	debian 12 / allegro5-doc