To implement CUE-OUT and CUE-IN in m3u8 that commonly used in HLS or DASH, you can simple identify #EXT-X-CUE-OUT: <duration> to insert Ad, and you can close its period by adding #EXT-X-CUE-IN like below:
#EXTINF:12, 1080p_72020201006T075438_00073.ts #EXTINF:12, 1080p_72020201006T075442_00074.ts #EXTINF:12, 1080p_72020201006T075446_00075.ts #EXTINF:1, 1080p_72020201006T075449_00076.ts #EXT-X-CUE-OUT:10.00 #EXT-X-CUE-IN #EXTINF:11, 1080p_72020201006T075450_00077.ts #EXTINF:12, 1080p_72020201006T075453_00078.ts #EXTINF:12, 1080p_72020201006T075457_00079.ts #EXTINF:12, 1080p_72020201006T075501_00080.ts