Can dupli groups time offset manipulate time?

Can a group be time manipulated by using dupligroups/timeoffset and perhaps keyframes or the IPOs? I was thinking of setting the time offset value at say 40 in frame 100 and 45 in frame 500, that would exteeeend the original group animation very much slowing it down. It is just an example. Is this somehow possible or is it only possible to have ONE time offset value pr. scene making “local time” possible but not exactly “time manipulation”.