you should focus on finding a bottom if u invest in index

if you invest in individual stocks, their bottom and market bottom are highly unlikely to overlap each other, For example, I would like to buy isrg, I am wondering when it is a good time to buy. I missed it years ago, thank God, it is coming back down, I want to be in this time but I am hesitating, when do you think I should pull the trigger? DivG? thank you. I can't think of a better strategy than average in.