Crap... In the veins of 'can't drink coffee after 6PM or I will not fall asleep'.
The first thing I do in the morning is drinking coffee and the very last thing I do before brushing my teeth is emptying my last cup. I always fall asleep within 5 minutes (much to my wife's irritation I may add)
If I am tired I'll go to sleep in broad daylight as well, it is all a matter of being able to deny yourself the luxury of stopping at a thought, spin them around and you'll fall asleep in minutes... stop at one of them and you can spend hours...