It is always a good time to start buying bitcoin if the money that you buy is an excess of yours because anytime the value of bitcoin may increase or rise. You don't need to buy bitcoin if the capital you will invest will be your source to finance your expense. The tendency is you will use it even it will result to a loss because you don't have any emergency fund to pay out your expenses.
I think that at this time if you buy bitcoin the risk will be very high, you can see that bitcoin prices are dropping sharply in the past few days and when touching the $ 6200 level, bitcoin prices have increased again, now Bitcoin prices are heading for $ 6400. I believe that bitcoin prices will continue to fall sharply at any time as you can see that buying power is weakening and prices for altcoin are beginning to fall.