When is the best time to buy Bitcoin?

Hi, I honestly don't know anything about Bitcoin or cryptocurrencies. But in a few months I'm applying to university, and I'd like to spend some money on Bitcoin to generate income in the long term. I know there are many cryptocurrencies that are very volatile, but... I don't really know much about Bitcoin. What are good times to buy? Should I buy when it's going down and people are selling Bitcoin? Or wait a bit longer until it starts to go up and save it for later?