The best way is to create an app or a website that connects to paypal which automatically allows customer to call or create ticket as well as charge the customer based on timings. For example if the customer open your website or app during day it would be X dollars and if they visit it at 2.00AM then X+Y Dollars. I would not advise subscription model if they do not frequently call you.

Bitcoins were designed to be – and, in many ways, are – the perfect digital currency: they’re frictionless, anonymous, and cryptographically astonishingly secure.Those strengths are also weaknesses. No one wants to risk losing millions of dollars worth of currency overnight, just because they were outsmarted by some computer hacker. Bitcoin isn’t the future. But it has helped to light the way of possibilities in creating a global currency..