Of course investing at the appropriate time is better than just jumping into the market because the money is available. As far as cryptocurrency is concern, if you enter at ATH, you might hit a retracement that you might be surprise will change the direction of the market against you. Take for example with bitcoin, people bought at ATH in December 2017/early January 2018 with the expectation for further high highs but market crashed. Hence, for those people who invested then, it was a wrong timing and so, they are either holding with losses or have sold with outright loss.
Well, I wouldn't say "any time" because that would be too broad of a description to denote when is the best time to invest. I think, for an investor, there should be factors that should delineate when to invest. For some, here are there considerations: (1) The status of the coin that is being invested upon. Is it gaining, is it falling, or is it beginning to gain? Those the questions that some consider as guidelines. For me, I usually consider those coins that are beginning to gain because I don't intend to wait too long before I can cash out on my investments. I tend to buy those that are beginning to show good sings of increase so that after a couple of weeks or a few months, I can get the most bang for my buck. (2) The amount of money you're willing to use to invest. Some people tend to jump the gun on this aspect because the common idea in this market is that we should buy as much as we can when the coin value is at its lowest; however, some people forget the fact that it's not a surefire hit if one coin has decreased in value, especially the question of when it will regain what it lost. Some coins don't recuperate from it, and thus, you will be left with a lot of lost asset as an investor.