The best time to buy more valuable altcoins is now. The market is still in the recovery stage with a lot of these valuable coins like Ethereum, Ripple, EOS, etc selling at relatively low prices. Seize the opportunity to buy more now and hold for the imminent bull market.
I think the market will stay low for a long time, at least until the end of this year. So I will not buy with all of my money, just a part and wait more time. If the price fall to lower, I can buy more coins with the same money.