Its correct depending on what framerate the scene was animated in. If you go to animation preferences > settings it will show what frame rate has been used for playback etc, this is the frame rate it will adopt when creating playblasts etc.

So if you have an animation which you have been previewing at 30fps and it looks good then putting 0.5 in as a value will look correct at 60fps, but if you havnt changed the settings from the default value of 24fps for playback (film standard) then it probably wont look correct.