Remove "\t" and change "Length" to "Duration"
Maybe "\t" can be removed from these two strings.
And maybe "Length" should be changed to "Duration".
There are some other stuff like videoControlsLengthLabel
and videoControlsLengthValueLabel
that might need to change also if changing from length to duration.
https://gitlab.gnome.org/GNOME/gnome-subtitles/-/blob/master/src/Glade/MainWindow.ui#L1270
https://gitlab.gnome.org/GNOME/gnome-subtitles/-/blob/master/src/Glade/MainWindow.ui#L1369
"Length\t"
"Sets the subtitle Start and End while the video is playing. Keep the button "
"pressed for the duration of each subtitle.\t"