Genie garage door opener light wont go out


I have the Genie Garage door opener Pro 88 (1/3 hP) that probably was
with the house... ca 1992.

The thing works perfectly but the light timer doesn't seem to work. The
light is
staying lit indefinitely.

Nothing obvious to me but I don't know anything about the operations.

Anyone have access to a Manual or know why the countdown timer isn't

There must be a place to adjust the timer?

Thanks in advance,