Electronic – IR receivers: how to interpet “Max. Envelope Duty Cycle vs. Burst Length”

ladyada has a discussion about ir pulses over on her page detailing the design of the TV-B-Gone Kit she sells. It might be of some use to you.

EDIT: There's a brand new tutorial on ladyada's site discussing how to build an IR decoder in even more detail, which has just been posted today: IR Detector

From the quotes you show, I would assume that "gap time" is not the time from the AGC pulse to the data start, but instead the gap from end of data stream to next AGC pulse. Think about it: The AGC pulse sets the sensitivity level, and the data should come right after that. If the gap is too big, then the AGC circuitry will have time to recover, and thus the data will not be decoded in context of the initial burst.

The gap time between codes is there both so that the AGC can recover if you move the sender, and so that the decoder can easily sense the difference between successive codes versus a very long pulse train.