-1
Not needed, no bloatware pls. When you press shift+tab, steam overlay will pop up. At the bottom, there is a clock. Choose timer option and set it to 20 minutes. Done. If that's too difficult, alt tab and look at the clock. Wait 10 minutes. If that's also too much, press F1 and look at the in game time.
If anything, maybe add feature to watches where it does a /me and tells you the time. and maybe setup a timer and stopwatch feature on your rolex, could be used for street racing, flexing your drip, whatever. That'd definitely be cool and would add roleplay.
But like everyone else said, there is steam overlay.