Legal double post.
(Yeah, late) Yeah, I don't know how to use GIMP that well.
I forgot to tell you this earlier, but here's a quick rundown:
If you want to set the time that a frame plays for in The GIMP, add (xxxms) at the end of each of your frame names. The "xxx" stands for the length of time your frame will play, and "ms" stands for milliseconds. The default playtime for each frame in The GIMP is 100ms, but this can be changed by simply morphing around the number. If you wanted the frame to play for a long time, you could name your frame "Frame 1 (replace) (500ms)" (without the quotes). If you wanted it to be faster than usual, you could name your frame "Frame 1 (replace) (75ms)".
The "(replace)" in the above examples just means to replace the previous frame with whatever is in the current frame in order to prevent the frames from bleeding into each other.