The best way to learn more about the alarm settings is to read the "How To Use" section of Wake Up Time Help, which can be accessed from Help menu.
In general we usually suggests to go step by step with the alarm settings. First set the alarm five minutes ahead of the recent time. Make sure you pay attention for the day setting. Press sleep and at the time of alarm, the sound will turn on. This is how the app supposed to work. Then set it for one hour, and if it still works you can surely set it to your morning time.