all three Cat Quest games, can be done pretty fast if you don't care to 100% or play again by new game plus.
(there's new game plus, stronger enemies, higher level equipment, and Mew mode which is modifiers thrown in, LOTS of replay value, 2 and 3 are co-op)
Trine games 1,2,3 are pretty short i beat all three back to back in one day in co-op (faster WITH more players, even 2 players makes trine 1/2 a joke you can fly over everything in the game literally)
child of light, if you gun through it on normal, is pretty easy, wiiU version took me 6 hours to beat twice with new game plus (higher level enemies)
Fairune collection, 3 very short games (Zelda like, no attack button you just tackle enemies to damage, LOTS of puzzles, may need a guide)
Mario RPG is one of the SHORTEST RPGs out there, SNES version took me 9 hours to 100% everything in it, switch version has an easier mode