How do I remove night footage from 300 days of Time lapse video
Using ffmpeg, a command line tool, you can use

ffmpeg -i in.mp4 -vf select='trunc(mod(t+2,3))',setpts=N/FRAME_RATE/TB -crf 23 out.mp4


The select filter is used on the video stream. This filter evaluates the supplied expression on each frame and keeps the frame if the expression evaluates to a non-zero value.

The expression used is trunc(mod(t+2,3)). The modulo function returns the remainder of the first operand when divided by the second. The first operand here is the timestamp of the evaluated frame. The truncate function truncates that result to an integer. If it is zero, the frame is discarded, else kept.

e.g. for a 25 fps video

t       t+2      mod(t+2,3)       trunc(mod(t+2,3))    select
0.00    2.00     2.00                    2             KEEP
0.04    2.04     2.04                    2             KEEP
...
0.96    2.96     2.96                    2             KEEP
1.00    3.00     0.00                    0             CUT
1.04    3.04     0.04                    0             CUT
...
1.96    3.96     0.96                    0             CUT
2.00    4.00     1.00                    1             KEEP
...
3.00    5.00     2.00                    2             KEEP
...
4.40    6.40     0.40                    0             CUT
...


Since you want to 'collapse' the video by removing the night time portions, the setpts filter is added to make all the kept frames continuous i.e. after the frame at 0.96, the next kept frame (2.00) will have the new timestamp of 1.00.

The video has to be recompressed since a filter has been used. For MP4s, default codec is H.264 and default encoder is libx264. The -crf 23 sets the bitrate control method (CRF) and value (23). Lower values retain more of the source quality at the expense of larger size. 18 to 28 are typical values.

You can get a ffmpeg binary for your platform from https://ffmpeg.org/download.html. Always get the latest nightly or snapshot build.