The GIF_DelayTime value must be converted to an ImageDelayTime value to make it work at run-time. It appears that the GIF_DelayTime is relevant only when saving to a GIF file. Is that correct?
BTW, I would suggest to make this conversion automatic. I see no reason why it should not be automatic.
If playback is in TImageEnMView, then TImageEnMView.ImageDelayTime specifies the playback time (which defaults to GIF_DelayTime for GIF files).
To change the playback time when viewing you should set TImageEnMView.ImageDelayTime. To change the playback time when saving you should set TIOParams.GIF_DelayTime (or TIOParams.ImageDelayTime).