Hard to time the markets buddy. So can't say exact when to, but any dip would be good. It was near its old ATH in satoshi value, them came down from there. I think it would be a good buy now, I don't expect that old ATH value to hold long and it will slice through it.
The old ATH value will not last in the market and I'm sure it will change someday although not soon, because everyone still has a lot of faith in all the good cryptocurrencies as well as the very good ones in the market, so don't be discouraged by that