Personally, I have not noticed a difference, however I only take 250-500 mg per day. I've had a few nights where I had so much energy, I couldn't easily fall asleep. But I can usually correlate those days with excess caffeine consumption.
I think as research goes on we might find that 1,000 mg of sublingual or liposomal NMN to be far more potent than the 1,000 mg of ingested NMN originally recommended by Dr. Sinclair. In addition we have to factor in the transdermal products entering the bloodstream.
As a result I personally avoid taking NMN after 3PM or 4PM latest, same rule for me with coffee although when younger I was one of those people that could have a coffee 30-60min before going to bed and sleep fine (or at least I thought I did at the time). I discovered later in life that I have the gene that processes caffeine quicker than most.
I am still experimenting with dosage of NMN. I think you can build up NAD+ in the system, so that lack of sleep from too much can creep up on you and then persist until you get it down to normal levels.
I was taking 1 gram/day a few months ago and doing fine, but at some point my system apparently got overloaded with NAD+ and I couldn't sleep. This dragged on for awhile until I decided to completely reset and purge my body of it for several weeks and start over. I finally returned to a normal sleep cycle after almost a month, so started over again with a low dose and kept increasing slowly to figure out where my top end tolerance was. It seems to be between 500 and 750mg. If I'm on 500mg, I'm okay but when I up it to 750mg for more than a few days the lack of sleep returns. Not insomnia but only getting around 5 hours of sleep per night.
I read some months ago about a possible skin test to measure NAD+ levels on the horizon. This is really what is needed - a way to test NAD+ levels to see where you're at.
Interestingly, I also have been having crazy, really vivid dreams that I can remember much better upon waking than before. I don't know if this is due to the NMN or some other supplements I've started with (ESS60 comes to mind) or some synergistic action of a combination that I'm unwittingly taking. For maybe the first two weeks or so, I would wake up over and over all night with wild dreams, lie awake for a little bit and go right back into it. It seems to sort of be toning down; I'm still getting the crazy dreams, but it's not waking me up as much in the middle of the night now.
The frustrating bit is that I've been trying to go to bed early so I can wake up on my own without an alarm, but without looking at a clock (and potentially really waking myself up), I have NO idea if it's actually time to get up, or just another short wakefulness episode.
I'm still trying to figure out my optimal dose as well.
So if I took it before bed, i think i would be missing out on the benefit of taking it before i begin my day,
I take a bit of NAD+ immediately before exercising in the morning and top up with the daily dose of NMN straight afterwards.
I hope this generates the maximum effect.