i would say good luck trying to predict any reliable trend such as that. There's weekends that the price go down and weekends the price goes up, theres always week days where the price goes down and the price goes up.
To answer the question of when is a good time to buy, a good time to buy is when you have some set prices in mind and if/when btc reaches that price.
I like how you think. Some people just think they have to look at a chart for a few minutes and can predict the future.