This subtitle-format (I do not know .tmd file type, but maybe TMD just means h:m:s or Hours:Minutes:Seconds in your language?) seems to include only start-time of the individual subtitles and no end-time or duration is it?
In that case you could perhaps set "Maximum subtitle display time" to another value.
Check out (rightclick) > Options > Preferences > Subtitles
(Just below the window with the check-boxes at the right hand side.)