Am I doing the shadowing technique wrong?

I get that it's supposed to be a very effective way to improve your pronunciation, intonation, etc. but I'm kind of struggling with it.

I basically listen to the sentence a couple of times, pause the video and repeat the sentence, then rewind and try saying it simultaneously with the speaker in the video. So listen, repeat alone, then repeat simultaneously.

This is how all the tutorials on youtube have taught me to do it, but is this right? I guess it just "feels" like a total waste of time lol. Not to mention I still get the intonation slightly off which I can recognize but don't really know how to fix, but people just tell me to move on and that it's a part of the process. I'm just confused how this technique is supposed to help. Like is the improvement supposed to be noticeable over time?

Also since I'm repeating and rewinding so much, it takes me like 20 minutes to get through like 1-2 minutes of a 30 minute video. Is this fine? Like if I'm aiming for 15-20 minutes of shadowing practice a day do I just shadow for the first 1-2 minutes of the video and then just watch the rest without shadowing?

Bit confused on how this all works and how it's supposed to help me