Yeah, when you're feeling that tired, it's just hard to pull off effective LD practice. For a million different reasons. This one gets me all the time. If fatigue were not an issue, there's no question that I'd go for an LD and WBTB every single night. But some nights I just take it easy. I like to make at least 3 nights a week just simple sleep w/ only a low-key WBTB. (I've found that WBTB has become pretty natural for me now, unless I'm very fatigued.)

You're right about the caffeine hitting full stride at about 30-60 minutes. That's going to be somewhere around your peak plasma level, and after that, caffeine's elimination half-life is actually pretty high, so you'll be amped for a while. It's hard to know just the right trade-off! You're way closer to figuring it out than I am (since I use the caffeine slightly less frequently, and wasn't the guy who came up with it.) I've been changing it up by using no aids most nights, then rotating in either B6, caffeine, or my once-weekly galantamine. That keeps things interesting too.

You've got to be a bit amused that 2 days without a lucid feels like a dry spell now. You are obviously doing great. You'd probably benefit most from simply getting more sleep, but that's easier said than done. One idea is that you could save caffeine (or whatever aid) only for nights where you will be getting a certain amount of sleep. That'll encourage you to get to bed on time and also help keep you rested when you just can't quite do it. The downside is that it can turn you into kind of a sleep fanatic.

Speaking of that, I even got these blue wavelength-blocking glasses. LOL. I'll have to post a pic of these things sometime. They are cool let me tell you!