Build the timelapse once in highres media. In something that supports it natively. Say After Effects. Make it run the longest you could possibly want it (that way you can speed it up further if desired). Then burn in the timelapse (i.e. render it out into a master quality codec). Import that into Avid and use however you'd like as your new master source. Much easier to deal witha 20 minutes long speed up clip than 20 hours of raw footage.