I'm assuming that this is must be a brand new feature of the Live Channels app because I haven't seen any other reports involving this new Time Shifting feature yet. If my specific setup makes any difference, the Live Channels app is installed on my Nexus Player, which gets its cable TV signal from an HDHomeRun Prime. I didn't have much time this past evening to test out this new time shifting feature yet, but it's a nice, welcomed addition, that's for sure.
I'll have to check this out when I get home. I wonder how much space there is (time-wise) without hooking up an external hard drive.