There's no "setting " of the defrost timer, it keeps its own time.

Your unit is comprised of a 3 component defrost system

including the timer, bi-metal, and a heater.

If you have excessive frost build up on the evaporator

coils or it's clogged completely then yes you have a defrost

problem.

now all you have to do it figure out which of the components you need.

the defrost timer is located in the control housing inside of the

refrigerator section and yes there is a hole there to advance the timer for testing.

Item # 646 on diagram below

if your coils are still clogged all you have to do is slowly advance the timer

clockwise with a screw driver "click by click" and when you reach the defrost mode you will

hear the compressor and freezer fan shut off.

When in defrost mode if the heater thats around the evaporator coils

imediately comes on the you have a bad timer. the heater can be checked by

touch "be careful" or with an amp meter.

If the heater is not getting hot then you either have a bad bi-metal

or a bad heater. the heater can simply be OHM'd out for continuity

and so can the bi-metal (as long as it's still covered with ice/frost)

If it's not you can submerge it into a glass of ice water for a few minutes.

Timer Link (if needed) Bi-Metal Link (if needed) Heater Link (if needed)

Source: How To Set Hotpoint CTX24GLR Defrost Control