Ok I short changed that a lil. Maybe like a day or two lol.
SMB 1 and 2 can be done in a couple hrs if you good at basic platforming.
SMB3 is gonna take 4-6 I'm guessing
SMW would probably be the longest, especially if you try and get all 96 exits. There are multiple times within that game that you can skip entire areas and go straight to world 7 to beat the game. You can legit "beat" the game within 45 min if you use some of the star warps.
There's no fun in that though. I would try and get all 96 exits...that would take prolly 10 hrs or so if you know what you're doing