If the time is stuck at 0:00, it would suggest that the PC has either high memory or CPU usage and there is not enough of one of these available for the recording to actually begin.
If you have a hardware encoder available, make sure you select that as it will take some of the strain away from the CPU. If you don't, the best option is the downloadable x264 option. which tends to use less CPU that the other two software encoders.
Closing any unneeded apps that are running in the background can also help. As can reducing the resolution or some of the graphical settings in the game.