While the right-click on screen menu only goes up to 5000 milliseconds, the OSD menu, accessed via arrow up or arrow down on the keyboard or remote, can go as far as you like.
Also, once you have added a bit of an adjustment, for large changes it is easy to stop playback, display the [Playback Info] tag, and adjust the setting in there. It will be obvious how to when you look at the tag. The adjustment is also in milliseconds.
Of course if the Subtitle timing is actually that bad, you might want to adjust it in the source file, so that the changes move with the file permanently rather than rely on MC making the adjustment during playback. There are tools available that can adjust Subtitles timing for various Subtitle formats. Google them.
Or find a better Subtitle file, if the Subtitles are in an external file, such as an srt file.
