Thats a bit simplistic.

Caffiene has a half life of 5 hours, which is to say in 5 hours your average person will have metabolised half the dose. So if you have 200mg at lunch time, at 5pm your still feeling the effects of 100mg, it could take 10 hours to completely clear your system. If you're sensitive to Caffiene,have a low tolerance or metabolise it slower you might have trouble sleeping before midnight.

I have a biblical tolerance, I'm up at 4am for work and I'm on a pretty serious cutting diet. I have my preworkout can at 3:30pm and have no trouble sleeping at 8:30 to 9pm.

What if I don't wake up until 2pm?

As a woman of an age dealing with unfortunate hormonal fluctuations, I'm holding myself to this. It's almost frustrating in the way it's paying off.

I've been riding the cycle of shitty sleep leading to excess caffeine, leading to shittier sleep even taking melatonin, leading to even more poor diet choices. I suffered through a day where I denied myself afternoon caffeine (stopping at noon, where previously I thought 3pm was close enough) and had a sucky day. But I slept slightly better that night. Holding myself to this, each night's sleep has been slightly better, and I feel like I'm making smarter decisions again.

It's still too early to say if it'll be a long term solution, but this last week I've started taking small doses of l-theanine. It's the stuff in tea that's supposed to help you relax. I found 200mg chewable tablets that I break into 1/4-1/3 pieces. I take a little in the morning and some before bed, and am overall feeling more relaxed. I've slept beautifully the last few nights without melatonin, but with my track record I want to see that hold a good month before guiding the l-theanine all the credit.