Normally footage is shoot at 1 frame every minute or so. Then you capture that and normally still speed it up. So if you recorded over 9 hours you would have 18 minutes of footage (540 frames) So if you wanted to have it play in 90 seconds you would speed it up 1200%.
So if you have real time footage you would want to leave just one frame every minute or two, simply cut out 29 frames, close gap, frame ahead one, remove 29 frames, close gap and so on. Export this as a self contained movie, bring it back in and speed it up to desired duration and you have a perfect time lapse, no frame blending is ever needed.