I do manual check up and noticed that there is no significant day for the prices that depend solely on date. But time surely will affect this, as some of the traders arent online where some of the traders are active. Imagine if some of those active traders are sleeping on the time you are active you wont see any much difference as volume is stable. I noticed it when I'm using Binance platform. Anyway I got the point why OP introduced this as somehow related to my idea but explained in different way.
indeed no one can provide a guarantee when the right time to buy bitcoin because the price of bitcoin cannot be predicted but to be clearer the very right time to buy bitcoin is when the price of bitcoin falls, you can buy it and after that you can sell bitcoin when the price has risen to become expensive, don't let you overturn because when you buy at high prices it will only make you stuck in bitcoin.
while for an exchange that can be used to buy bitcoin I think you can buy bitcoin at an exchange that has an influence on bitcoin price movements, for bination exchange places I think it's enough but maybe you can try it at another exchange that has a good reputation .