Offset Youtube video timestamp

When using timestamps and taking notes from Youtube videos it would be helpful if there was an offset to the timestamp taken.

This could be implemented as a configurable parameter (offset) in settings (e.g. timestamp is always set at x seconds before the time the Shift+Cmd/Ctrl+Y key was pressed and/or it could be implemented as +/- buttons next to the timestamps so that it can be configured on the fly, like this:

Note: I am speaking of Youtube here, but the functionality would be just as useful on Vimeo embeds etc.