Since they are holders, they don't really care whether it's uptrend or downtrend as long as they think that a certain price is good to buy.
They will not sell after all so if ever a downtrend happened right after they bought, no worries as they will hold no matter what.
There is no definite answer about WHEN so try to make up an own decision by doing research and analysis.
When you do have that HODLER mind then you would definitely do such thing where buying up coins when you do think its cheap and
dont tend to sell no matter how high the price do peak out.This is truly a definition of being a hodler but it isnt really bad to consider
to sell out on peaks for you to secure out profits.Just like what happen on previous ATH where people should cash it out
then buy again when the price goes down in 3k levels.Rinse and repeat.
Only one solution for good timing to buy and invest with cryptocurrency when bitcoin and altcoin have been support price, maybe you must waiting for when your target coin to buy touch lower price and sell after break out to higher price.
Aiming for support? Everybody does but not all does have the balls to buy when the market is declining and thats a fact.