set the alarm for six o'clock

[sunsunmoon]

Merriam-Webster's Learner's Dictionary
▪ She set the alarm for six o'clock.

It's not okay to say "to" in place of for, is it?

 

[Rover_KE]

No. 'For' is correct.

Rover

 

[BobK]

...But if you're focussing on the adjustment, rather than the effect, it would be OK. So you could have something like 'She set the alarm for 6.00; but then she thought again and set it back to 5.45.'

b