From my little experience with the Bitcoin Investment system
Please don't call it an investment
system. Because it sounds like a scam.
the best time to buy the coin if you are targeting to make a profit in the bull run is during the bear run. The price is cheaper and you can make a good profit within the four-year circle. At this period you don't need to rush to buy because of FOMO but you can comfortably buy at your own pace using the DCA or other strategy that suits you.
Why bull run when you can do it on a bear market? It's cheaper and better time to accumulate on that period.
DCA might be the right choice when someone believes their investments will appreciate in the long term and experience price volatility on the way there.
DCA has always been the best choice for someone who believes on holding it.