One question before everything else: are you trying to get your sleeping schedule fixed/decent?
I think if you don't have a decent enough sleep sched, the alarm thing (WBTB) won't really be helpful since it relies on interrupting your REM sleep *insert technical stuff here hehe*, and if you have a very erratic schedule that's just all over the place, there won't be any REM to figure out, really. Does that make sense? I suggest establishing a (semi)ndecent sleep schedule first, you can try by going to bed at roughly the same time every night. Once you get a nice routine going, I am sure you will have much better success at doing WBTB (Wake Back to Bed).

Or, in the mean time, as you're figuring that out, you can take naps! Naps are great, as you fall directly into REM, and you dont have to wake up after 4-6 hours. :3

Check this out: WBTB Tutorial - Lucid Dreaming - Dream Views

Hope this clears things up a bit, cheers!