How quickly do payments show up in a PayPal account?

My business has set up a PayPal account to send quick invoices to people who need quick turnaround on design projects (i.e., so we can get some money in the bank from them before we start work). How quickly do payments show up in your PayPal account? (i.e., so that I can log in to PayPal and say, “Aha–they’ve paid us; let’s get to work,” or “those rotten cheapskates still haven’t paid us; tough luck for them.”
) Within minutes? Within a day?

I swear, I’ve searched up and down in PayPal’s FAQs, but I can’t find the answer (and I’ve only used PayPal once before, and I can’t remember how long it took).

I’ve had them show up in just a few minutes after I’ve entered them.

Yes, in my experience, it will be a matter of minutes.