Bitcoin accumulation can be made any time either by DCA or lump sum considering the investment plan and the financial status of the person but the best time to optimize accumulation is to leverage the opportunity of dip period because it's cost effective and it gives investors the opportunity to accumulate more volume of Bitcoin compare to investing when the price is high. Although, I may say that it's not advisable for investor to wait for dip before investing on Bitcoin because while waiting for dip the investor may have other financial needs they may tempt him to use the money, so it's advisable to start investing by DCA while waiting to leverage the opportunity of dip.
I think the majority are more into the DCA than lump-sum. Anyways some folks got the wrong impression of buying the dip, they feel that buying the dip means they should only wait for when the market falls before they seize the opportunity, that's a very wrong impression cause such folks would miss out on many opportunities in the process of waiting, what they don't understand is that the DCA can still be implemented and investor would still get a chance to buy dip on different occasions according to their plan, bitcoin market is so volatile so while implementing the DCA you must definitely come across lots of dips and seize the opportunity, that's far more better than waiting then miss many buying opportunity in the process. Anyways I believe that's why the majority uses the DCA more often than the lump-sum.