You mean that if the price of the coins have started to increase, that you want to start buying crypto? Why no just start buying bitcoin now? You can set certain amount to buy bitcoin weekly.
~snip~
Because of the attitude that is actually a characteristic of all those who adhere to the
"fast in, fast out" strategy, that is, the plan to invest their fiat in as short a time as possible, while making as much profit as possible. That's why we have something we call FOMO (fear of missing out), which is most pronounced during the bull run, when people buy the most, and they are usually focused on some number that serves as their exit point, such as $100k in the last bull run.
The OP is actually asking
"how do I know when others start buying so I can do the same" - and let him look for the answer in a possible price increase, although any (even significant) price increase does not mean that the trend has reversed, but that it may be a small pump with great prospects of pulling back.