^

There are many ways, using video-editors is probably the best one. Sony Vegas as a example has a feature where you can select a certain part and you then see how long that part is, other programs probably have similar features. If not, just cut the video manually and then see how long it is.

I frame count my runs with Avidemux 2.6. I use it to see how many frames long my run was and then I simply divide that count by my capture FPS of 29.97 to get the time of my run in seconds.