You can start buying right now, but don't buy all altcoin with your money. Just buy small amount of altcoin because most of them are cheap atm. 1 Week (might be) before the next fork happens is the best time to buy altcoin.
I think is not good to buy altcoin before fork mate. Why? Mostly people will buy bitcoin and leaving altcoin.
People buy bitcoin to get free coin after fork. So i think its not time to buy altcoin.