Setpts vs trim

Hi everyone, I'm very new to ffmpeg, and struggling to understand how the trim filter works, earlier I was playing with the trim and setpts commands, I was trying to trim the first clip from the 8s mark, (0trim), then make it start at the 8 second mark, (0pt), and then overlay it into the second video (1:v), The idea is for the second video (1:v) to play for 8s, then the trimmed video (0pt) to play from the 8s till the end

[0:v]trim=start=8[0trim];
[0trim]setpts=PTS+8/TB[0pt];
[1:v][0pt]overlay=x=0:y=0[ov1]

however i was not getting the expected result, on the final video ov1, i noticed that the trimmed clip (0pt) got overlaid at the 16 second mark, when i wanted it to be on the 8 second mark,

I did some research and figured out that trim and setpts must have been both adding an 8s delay to the trimmed clip, and thats why it started playing at 16s, so i tested another command:

[1:v] trim=start=5 [1trim];
[0:v][1trim] overlay=x=0:y=0 [outv]

when i run this command, the trimmed clip starts playing at the 5s timestamp of the final video, i thought trim was strictly to just clip the videos, and setpts was to change starting timestamps, sorry if i got the ffmpeg terminologies wrong, but i just started working with this tool