Know not to time the market, but will you buy at all time high?

It depends on the company and how familiar I am with it - if I don't know the company's business model well and I only invested based on reading the charts, then no. When you buy a stock, you have to believe in the company so much such that even if the stock price tanks, you won't panic and sell it. If you're buying it because of FOMO or you're not so familiar with the company/industry , I'd advise you to set a limit for yourself (e.g if the share price dips to X dollars, I'll buy Y shares).

Why not? There are constantly new all time highs being made, that’s how you earn money from the stock market.

The ATH of today might be the lowest the stock will ever be in the future.