In Essentials, the player's start date is saved as $PokemonGlobal.startTime and the play time is Graphics.frame_count. I really don't support the MMORPG version, which I believe was branched off from Essentials years ago and I have no idea if it's updated or what it does.
I've just tried it in Essentials, and while you can open the pause menu just before the NPC notices you, saving and loading won't stop that NPC from noticing you immediately, which means you couldn't get past a roadblock that way.
Still, you shouldn't be able to open the pause menu at that time anyway. Thanks for the report and the fix (which I also applied to using a registered item).