HDhomerun not allowing Live TV

Not sure what I am doing wrong but I have the Plex server and Media player installed on a Windows 10 computer. Everything works very well. I purchased a HDHOMERUN dual TV tuner device. I also went Premium on Plex.
I plugged in the HDHOMERUN tuner and configured it. I also went to Plex DVR (Beta) setup and it found the device immediately and I went through and completed the setup. It started and completed the program guide setup perfectly. Looks really good.
The only problem I now have is that if I select a program that is “On Right Now” there is no “Play” button to view it live, only a record facility. How to I watch live TV in Plex?

Only Android TV and iOS apps are supported for Live TV
https://support.plex.tv/hc/en-us/sections/205778607-DVR-Live-TV

You also should change your username to be something different than your email. which you can do here https://app.plex.tv/web/app#!/account

So is the restriction on Windows being used to watch live TV a Plex restriction or a HDhomerun restriction?

It is not really a restriction.
It is a new feature and Plex started with iOS and Android TV devices. Other platforms are coming.
No, there is no timeline. Plex does not give timelines.