I have an HP laptop that has MX350 graphics card and the screen is 60 hz. I used Aegisub 3.4.0 to fix the timing of the subtitle lines. I set the end time and I pressed d to listen to the last 500ms of the line and I pressed w to listen to 500ms after the end time. If I had set the end time to be too early then I will hear the ending of the last spoken word when I pressed w thus I have to advance the end time. After that I pressed ctrl and p to play the line. If I couldn't tell if I line ended exactly when I heard it and I don't know if it exactly ended when a person stopped speaking or a bit before then that means that the end time is too close so I added a .05ms delay to the end time so it became obvious that the line ended exactly when the person stopped speaking.

I am using MPC-HC with madVR on the HP laptop. I played the movie in MPC-HC to verify the timing of the lines. If there were any issues in the timing then I fixed them in Aegisub and I replayed that part again in MPC-HC. I had fixed the timing of 12 subtitle files. There were no issues when I played the movies on the HP laptop.

I recently bought a Lenovo laptop that has a RTX 4090 graphics card and the screen is 240 hz. I also used MPC-HC with madVR on the new laptop. The problem is that I when I played those movies on the Lenovo laptop in MPC-HC then for a lot of the lines it sounded as if they ended before the person stopped speaking but there is no problem when I pressed w in Aegisub on the Lenovo laptop. I tested the movies in SM Player and also by playing them in Aegisub by pressing ctrl p. The problem is there. Also, the problem is other movies that I had previously fixed their subtitle files.

I think that the problem happened because the Lenovo laptop is more powerful than the HP laptop and 240 hz is faster than 60 hz so it made the timing issues more obvious because the lines are played a bot faster on the Lenovo laptop. Now I have to again fix the timing of the lines on the new laptop and I again add a delay to the end time so the problem went away and it became obvious that the line ended exactly when the person stopped speaking.

I have an old TV which is 60 hz and I connected it to my laptop by HDMI and I mirrored the laptop screen to the TV. I ran a game on the Lenovo laptop and the fps was 140 fps. I don't think that the TV is showing the game at 140 fps and it dropped frames so it's 60 fps.

I want to ask is it ok if I stay on duplicate the screen and I fix the timing of the subtitles using the TV while it's playing the movie at 60 hz or should I set it to PC screen only and I fix the timing of the subtitles using the laptop while it's playing the movie at 240 hz? I am worried that if I use the TV then the same problem that happened when I fixed the subtitles on the HP laptop will happen when I use the Lenovo laptop and I play the movie at 240 hz.