How to read time from the PC?

I'm working on a project which if the time is within a certain range, it does something. I know how to use IF statements, but:

I'm wondering how do I read the time from the PC the Arduino is connected to without connecting any shields?

What Libraries do I want or need?

How would I write such IF statements, where it does something when the time is in a certain range?

Generally people use a RTC such as DS3231 module. Set it once.

Check PLX-DAQ. I understand it has two way communication, and that may include time.

ESM4 has a sample sketch that does exactly that (along with other things) so you can get the date/time onto the Arduino.