Best time to buy is when the market is bleeding too much,but as far as i can see these bloody reds arent yet profitable because the coins are still good though most of them are down,we still doenst have a 30% off from the value of each coins yesterday so i wont be so sure about this correction because it seems to be normal to me.
Maybe one should consider doing your home on market research,check the price movement, what specific coin your planning to put in your investment, this are just a few thing to consider before buying or putting in your investment. And always remember that market is Volatile, no one can predict or even speculate what next in the market trading. You, decide after review of the market movement, buy when the price is low. Hold on until the good price goes into the roof, then sell it.