For editing the "show" and "hide" times of the subtitles, the program does not accept the numbers of the num-block. If I change one digit, the program does not jump to the next button - I have to move the cursor manually. Moreover, I can delete digit, provoking parsing errors. Consequently, I usually user the notepad to set the subtitle timings.
In my opinion, the definition of an edit mask, where I cannot delete anything, when I enter a number (from keyboard or num block), the cursor moves on automatically.
Assuming a working overlay of the subtitles over the DVD, two additional buttons could define the current video position as start ("[") or end time ("]") of the currently selected subtitle(s).