Project Settings - Drop Frame

If you work in a 29.97 or a 59.94 project there are two ways to count the frames. Non-drop frame (unchecked) simply counts every frame, so for 60 minutes it will count 3,600 frames. The trouble is that doesn't take 60 minutes of time, because you don't have 60 frames per second, you only have 59.94 frames. So your project will end before actual 60 minutes of clock time has passed. I can't remember what the difference is exactly, but it's something like four seconds. To keep the frame count the same as clock time, the system drops frames in the count. It drops four frames every minute (two frames in 29.97), except for every 10th minute, when there is no drop. This way 60 minutes of timeline time is actually 60 minutes of clock time. If you work in television you'd better use drop frame.

Just to illustrate in a 59.94 project in drop frame this is the end of the eighth minute

This is the next frame number

This is only a thing for those ghastly fractional frame rates. It has to with how you count frames because the number of frames does align with the time in seconds. Fractional frame rates are a legacy from almost a century ago when color was added to analog tv broadcast. It is a shame that they persist well into the 21st century in a digital world.

Quite right. Thank you for the correction. 216,000 for the hour.