ffmpeg -ss 00:15:00 -i input.wmv -ss 00:00:20.0 -c copy -t 00:00:10.0 output.wmv
ffmpeg -i input.wmv 00:15:20.0 -c copy -to 00:15:30.0 output.wmv

REM  The first -ss seeks fast to (approximately) 15min0sec,
REM  and then the second -ss seeks accurately to 15min20sec
REM   -t: duration
REM copy:
REM timestamp format: HH:MM:SS.xxx