SM's about the same time as BW/2 (shorter if you don't try to catch everything on Route 1), just different circumstances. XY and ORAS were super fast and allowed trading as soon as you caught a second Pokemon if I remember correctly.
Sun and Moon, you couldn't trade until you gain accessed to the Pokémon center near the Pokémon School, so with the cut scene it would take a while.
X and Y was pretty fast and allowed you to do it from the moment you got your Pokédex, though bizarrely you couldn't access the PC till you reached Santalune City.
The Hoenn remake changed it heavily as in the original game you could trade from the moment you got your Pokéball but in the remake you couldn't until you help Wally the wimp catch his Ralt in Petalburg City.
Thankfully Pokémon Bank bypasses some of this problem but it still require access to a PC and Egg can't be sent over bank so I would be waiting awhile just to get Charmander on my team.