The best time of this is when you are catching the peak of the pump, but this is too hard to accomplish so as far as I know you can grab the coffee cream from the top 
near the top, at least.
I do not think that there is any specific time to making profit from bitcoin trading or investment, you just need to study the market and take a decision when you realize that now you can get some profit from your investment. I think that taking a right decision in right time is a very much difficult take. near the top, at least.