You should start buying alts now but always have some left until October 24. We should expect more altcoin dumping to come as the day nears to Oct 25. Do some research on the most promising alts that you can think of and start buying them. They could provide you good profit when money from BTC move again to alts market. The thing is, you should also save some BTC so that you can get some BTC gold after the fork. Covering both sides of the market would be very beneficial for you in the end.