I totally agree with you there's no exact time to buy bitcoin, talking about variable I think that is the main reason why most people think that there's always a specific time to buy bitcoin. as long as crypto market is concerned there's no stability in the price of bitcoin, sometimes it might be due to halving unlike as you said earlier. However I think there's no specific time to buy bitcoin, except you don't have capital to invest, but if you have enough capital you can invest in your convenience time.
hmm right!
There might not be a specific time since no one can perfectly time the market so there is no point in waiting, but there are specific methods for specific times when you wish to invest. Let's take the current price as an example, now if someone wants to buy Bitcoin when the price of Bitcoin is above $66k which is a very high price, they would think that maybe they should wait for the price to drop before they buy because it is currently too high.
They don't need to wait, all they need is to apply a method, and we use the DCA method in such situation. The DCA method is used to buy an asset with a portion of your capital at a certain price point and keep the remaining capital with you, when the price drops in the future, you can use the remaining funds to buy again, and you keep doing that until you have nothing left or you think it has reached the bottom.