It depends on the game.
Very much this.
Ever played Dark Souls. Or Baba is You?
It is a thin line to make a game playable but not too easy. But also not too frustrating.
I think the length of the timer intervall till you pop up the notification that help would be available is not very important. It also depends on what this will cost the player. Dignity? Achievments? Some kind of ressources?
Without knowing the scenariou I would suggest considering a one time help notification that the option is available in the menu or whereever you hide it and pop it up after a few minutes of non activity to remind the people not reading the manual that the level can be made easier / skipped (for a price. or even for free.)