Today's timelapse is built one half-hour at a time. Each segment is appended to the previous build. Files are rotated at 8am and 4pm, then the parts are assembled into the daily file and moved to the Archive.
1 image every 15 seconds = 240 images during the sunset hour (a half-hour before sunset until a half-hour after). Compiled at 30 frames/second, so each sunset hour produces an :08 video.
The daily timelapse is 1 image every 30 seconds (2880 per day) compiled at 30 fps. Each day's timelapse runs a bit over 2 minutes.