SpartanII's advice is solid here.  I will just add that you might want to work the SP before the vibrational stage.  Practice deep full body meditation until you can completely relax your entire body.  Even a single tense muscle can keep you from exiting.

If you go from SP to Lucid Dreaming that is also a worthy achievement.  WILDs are really awesome.

At any rate, this stuff is hard, and often takes years of practice & cultivation.  Don't give up.  You might want to recalibrate the time you need to invest a bit, but you seem like you are nearly there.  

If you wanna avoid falling asleep, you can try a cup of mate or green tea... or start an hour earlier, perhaps.