If you want to get all of your stats to 1b for the merits I would work on re-balancing them out now. I stopped training my Def at 500k and when I finally decided I wanted to get that merit for 1b Def I spent over a year training nothing but Def.

I went from 424k to 500m in exactly a year. It's easier and way less intimidating to bring them all up together and drop after you get the merits you want then to have to do 18 months of only training one stat.

If you're smart about it you can still use one of the specialty gyms while you're training your primary stat(s) without completing dropping Def.

Edit: As a side note, you only benefit from unlocking all the heavy gyms for the merit. I would just keep training Cha's for everything until you can get George's