al_set_timer_speed - Allegro 5 API
void al_set_timer_speed(ALLEGRO_TIMER *timer, double new_speed_secs)
Set the timer's speed, i.e. the rate at which its counter will be
incremented when it is started. This can be done when the timer is started or
stopped. If the timer is currently running, it is made to look as though the
speed change occurred precisely at the last tick.
speed_secs has exactly the same meaning as with