I need help understanding Generic Product Keys

I just got into using Virtual Machines and enjoying testing out different systems or software out on them. I have just decided to start playing around with Windows 8.1 pro recently. As I have been a mostly Windows 7 user the last 12 years now. I have always been used to Windows 7 3 day trial. I haven't run windows 8.1 yet, as I'm reading and understanding the install process and what to expect. The main question I have is, how long does the trial last for when using the Generic product key to do the initial install? I see many say to activate after the install with a genuine product key. But I don't see many people mention how long you could run windows 8.1 without activating before it would be locked out like Windows 7 would on trial runs. How long of testing would I get this way before being locked out? I like to test out lots of visual type features on systems for a while before committing to a full install of an os. So I would like more than 3 days with windows 8.1 if that is possible?

i think you can run win8.1 for more than 30 days though it will keep on nagging you to activate it