Use http://www.watchframebyframe.com/ and set your video to 60 FPS. Find out when your run started and when it ended. For example, if your first input was at .41 seconds and the run ended at .61 You do .61 - .41 on google and get your time of .20 seconds.

https://mattbraddock.com/yt-frame-timer/ this website does it for you

^that website is down now

This is a new useful tool that was made: https://www.speedrun.com/speedrunning/thread/09ofz