Honestly, alarms will mess up the whole thing I think. You'll be expecting an alarm so you may be shifty and wake up before it knowing it will go off. I would time about 15 minutes; if you can gauge that with your mind, then that's cool. I now can time how long I am lucid. I kind of use video game timing. Something like Grand Theft Auto 5(or Online). The timing is what, 30 minutes is a day(I could be wrong). You have to adjust your timing to your own world view. I can simply lucid dream a whole 15 minutes and wake. Though, I may be still lucid, I may fall back into a dream because this is my recreational creative time lol. But you can time. Create a stream of water and keep that in mind. There are may things. Hope this has helped.