Since the camera times out quickly (and powers on quickly) I would indeed not have that be a "session." But certainly if you don't shoot or even turn the camera on for hours should indicate the end of a session. Certainly going overnight. I even imagine a change in the colour temperature of the external light should count as a change of session if you are not in AWB. When the warning pops up, you can ignore it and keep shooting, or press a menu button to say, "don't warn me about this again today, or again ever."

Now in the old days of shooting most things in manual, the idea of forgetting sounds silly. But today even the most serious shooters make use of automatic modes, and forget sometimes what we've set.

I wouldn't mind warnings like:

* You're in a very noisy ISO (from last session) but the scene is quite bright. It would not warn you if you deliberately set high ISO recently. But it would save you from shooting at 1600 in daylight.
* You're still in 10 second timer mode after a long period of being off. I hate when I press the shutter and lose an action shot as it times down. Alternate -- take both the immediate shot and start counting down, and let me cancel the countdown (or not, in which case discard immediate shot.)