Does Privatise offer Both VPN and RDP? What is the relationship between the two?

RDP is native windows functionality. A dependency of that is the network connectivity (VPN) that Privatise provides for devices on disparate networks. The VPN secures this RDP connection.

Is there a time period feature in Privatise that requires users to login during certain hours and then browse freely thereafter?

No, there is no time period feature in Privatise.