al_start_timer man page
al_start_timer — Allegro 5 API
#include <allegro5/allegro.h> void al_start_timer(ALLEGRO_TIMER *timer)
Start the timer specified. From then, the timer's counter will increment at a constant rate, and it will begin generating events. Starting a timer that is already started does nothing. Starting a timer that was stopped will reset the timer's counter, effectively restarting the timer from the beginning.
al_stop_timer(3), al_get_timer_started(3), al_resume_timer(3)
al_create_timer(3), al_resume_timer(3), al_stop_timer(3).