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.
If we think that we want to invest Bitcoin, it's time to buy today because the price in the market is goes down. It is better to hold that coin and wait a right time to sale that coin so that we can have earn more profit for our future.