If you're not in combat then you aren't using the in combat hiding rule that grants the invisible condition, you're using the regular order of play rules and making checks vs the DM DC.
Again, the specific rule of the Hide action in combat overides the general rule of play. Same with the Infuence or Search combat actions. Or even attack or magic actions.
For example, if a PC sneaks up to a sleeping nobel and slits their throat, I wouldn't have them roll an attack, I'd set a DC for them to do so without waking them up. If they succeed, the target is dead, if the fail, roll initiative.