There is no best time to invest because it is just not possible to guess the best time to invest no one knows when you need to invest because no one knows when the price will go down or up so i believe it is not something like this.
There is in fact a right moment to buy Bitcoin but its very difficult to get it right which is why the most common advice in the forum is to buy bitcoin whenever you can afford it, don't worry too much about the price if youre planning to hold for the long term.