Re: Yes, it's a Samsung.
On Samsung's, time based events can "fire" before the scheduled time - even if Android documentation clearly says that this absolutely cannot happen ("later" - OK, "sooner" - NO).
And so when the event to turn night mode off fires - before it's time - the app doesn't "understand" that "the night mode is over, push needs to be re-enabled".
At least that's what my magic ball says is happening on your phone
We could try to schedule alarms for a bit later, but it would cause delays on other phones.
Re: Remind me where to do that globally though please. And for how often I should set it to check.
App settings -> mail, receiving -> "scheduled mail checks" and I'd recommend a 15 or 30 minute interval.