Uh-uh, even this is easier said than done. According to Coingecko, the ATH is $69,044.77. Does it mean to say that by the time Bitcoin's price reached $69,050.00, it's already selling time? I don't think so. So when is selling time? $70,000, $80,000, $100,000? We cannot tell. But if you're good enough that you've already made profit, then selling beyond the ATH is good. But don't fret if months after selling, the price continued to rise 20% or more.
You have to take note that the halving's full effect on Bitcoin's price happens at least a year from the halving itself. And the growth is considerable you wouldn't want to miss it. The peak of the growth every after halving is significantly higher than its halving price. So a new ATH is probably a low selling point.