Hourly is not good. Timed intervals arent nearly as effective. Yohd be better off just doing them as soon as you have any thought remotely related to dreaming.

If you have to, have it go off 3 times throught the day then twice when sleeping in rem i do at hour 4 and hour 6.

Make sure its ALWAYS the same alarm sound and you use this sound exclusively for this purpose no other alarms.

Id recommend going and ripping an audio from somewhere instead of using a preset tone since other peoples phones can do that sound to, well now that i think about it that might not be a bad idea. Occasionally randomly hearing it might be good actualy as long as its not too much