You can start buying little by little if you want or you can wait until the market reaches its bottom which we really dont know when. Because it is really hard to predict the market. It is really up to you if you want to start now.
Yes, buying from now-on but little by little will get anyone big portfolio in coming days as they could have big number of coins for same amount of capital due to very much cheaper prices of cryptos. But you need to choose the right coin because only very few coins will be having chances to boom in coming days.