Hi folks. A DM ruling has been requested via PM.
However...
Una:
My only concern is Minor Illusion is an action, and Hiding is an action
I'm approaching this in the same way I'd approach a PC running behind a wall. It doesn't take longer to move behind a wall than it would to move to that space if there weren't a wall there, and line of sight would be cut off. It's just that the gnolls (perhaps) don't know there's a wall there, or why there should be a wall there.
How effective that illusory wall might be... that's for DM to decide. But I don't think I'm attempting to Hide in combat.