Arbitrary skip increments

The skip forward/back/first/last settings can only be changed in 5 second increments, with the -/+ buttons.

Some podcasts have a fixed opening intro. Say the intro lasts 27.5 seconds, I would like to be able to specify a "skip first" value of just that. In any case, 5 second increments are too rough. Why don't we give the user finer controls?

Start by locating the skip forward, skip back, skip first, and skip last settings and their current five-second increment controls. Check how values are stored and displayed, then verify that users can choose finer values such as 27.5 seconds for the opening intro and for the other skip settings.

Written by the indexing model from the issue text.