Following your example, I adapted it to skip an arbitrary number of seconds at the beginning and at the end of the audio file.
-A;$div($add($mul($cut(%length%,$sub($strchr(%length%,:),1)),60),$right(%length%,$strchr(%length%,:)),-B),60):$mod($add($mul($cut(%length%,$sub($strchr(%length%,:),1)),60),$right(%length%,$strchr(%length%,:)),-B),60)-
Now it becomes difficult to follow this code, but, for your understanding, the formula is (min*60+sec-x)/60 : (min*60+sec-x) mod 60
It works for durations shorter than 1 hour, otherwise you have to include the hours in the calculation.
Adapt it to your needs as follows:
A is the duration you want to skip at the beginning. Format in minutes (ex. "0:25" without the quotes).
B is the duration you want to skip at the end. Format in seconds (ex. "29" without the quotes)
A useful Tip for users of this component: I often listen to full length DJ Tracks which usually have a long intros and outros for syncing mixing and transitions. When i listen to such tracks i normally want to skip the first and the last Minute of the track.
Setting the Skip Tag for the first Minute is no problem with this component. Setting the last Minute is the trickier Part because you have to calculate the Time one Minute (or whatever you want to skip)
i solved this with the "Automatically fill values..." Tool in the Tag editor Window.
i chose source -> Other: and used this script
-1:00;$sub($cut(%length%,$sub($strchr(%length%,:),1)),1):$right(%length%,$strchr(%length%,:))-
Pattern is then the Tag Name
%skip%
With this examples foo_skip skips the first and last minute of each chosen (tagged) track