[hypotyposis]

Yep, that sounds about right to me. In my experience, transcribing meeting notes doesn't last nearly as long as the meeting but takes up a substantial amount of time; extra items are generated as I read through the notes and think about what was discussed again, which adds yet more time. My best experiences with this kind of stuff has been when I did that consistently during my weekly review and followed good GTD practice. I've been debating getting one of those fancy e-pens to avoid having to actually go through my physical inbox every time I need to transcribe notes, but I think that's more gadget envy than anything else.
Do you do weekly/daily reviews and if so how much time do you allot to each? This might be a place where you could fit in the transcription.