Apart from buying bitcoin during bull market, I think buying any other time can be profitable. The bitcoin market has trend, especially to the long time investors.It is always advisable to buy bitcoin when the price is low , so that when the price rises you will be able to make some profit.

When you buy your bitcoin when the market is already roaring ,it can make you loose money. Some people would continue buying bitcoin any time the price dips, and following  market news will go a long way because you will always be informed when to buy, more especially when the market is in deep red.