For long term hold, it is never too late to buy any coin at top 5 marketcap, but if your plan to short-mid term hold, i suggest to wait next correction.
Correction is probably hitting in as we speak. I assume there will be a number of traders looking to sell at the next higher round figure namely 50k USD at the current scenario but even before that happens there can be a crash if they all become last-minute-impatient and start increasing selling pressure. Today's price I would rather advice to hold and wait for the price to come down because it is bound to and then the dip would be worth buying.
Dip is a part of trading and whenever someone is buying a token, he have to get the information about the token which he is going to buy and he will get that information by searching about the tokens, their graphs, their charts, their history and more about the coins own beneficial aspects, then only you can get profit and entry.
You will get the profit only if you sell the asset at a higher price. No amount of research can change that. Importance of research is elsewhere - choosing the enter/exit points and the time of holding.
It doesn't matter whether it the really the bottom if he is up to wait for another spike because Bitcoin always goes up.
Yeah but just my thoughts that if Bitcoin drops from 50k USD, the chances of seeing 50k+ will take longer than 6months now. So buying at this price is risky.