it all depends on the research you do, if the altcoin that you are researching has reached the lowest point then I suggest you to buy immediately ... but if you still doubt then please wait until it really reaches the lowest price, don't ask anyone for advice because all depends on the research you do.
In fact it is very difficult to identify the perfect moment in which to buy a coin, because given the great uncertainty of the market there always seems to be room for a further fall. Even the traditional technical analysis tools do not seem reliable enough to determine that "lowest price", so it only remains to be very cautious and not rush to buy altcoins in times of uncertainty or doubt.