Some terminology, because I don't know the "usual names" for some of these things:
1. Playback Indicator - The little ball that sits on the timeline for the song that indicates how far in the song you are
2. Playback Bar - The bar that the playback indicator sits on
Imagine you have the current scenario:
1. You press down on the playback indicator in order to drag it to earlier/later in the song
2. You realize that you no longer want to skip later or earlier in the song, or that you accidentally pressed on the bar in the first place
Currently, there is no way for you to have the song return to what's playing now without a small blip in audio. The best thing you can do is approximate the time as well as possible, which brings you back to within a few seconds, but still causes an audio cut. This audio cut is very minor, but I find myself running into this several times a day and it gets a little irritating occasionally. Ideally, it would just keep the music playing.
Have Spotify keep playback going from the current point if the user releases the playback indicator within ~5 seconds (or a small percentage of the playback bar) of the current playback point.
The time range should be big enough that the user can consistently hit that time range if they want to keep playback going with no audio cuts, but small enough that the user is still able to go back or forward small time intervals.
In fact, a strict time interval across all songs might not be the best idea, because, due to different lengths, the physical distance the user would have to hit would differ for each song. Longer songs would require more precision, whereas smaller songs would require less precision. A better approach to this may just be to make it a percentage of the progress bar - Maybe 5% each way from the current point of playback would be a good compromise?
However, then, what if you want to rewind about 15 seconds in a 15 minute song? You'd probably have to go back by at least 30 seconds if this exact method is used.
Maybe make it percentage based for shorter songs, and time-based for longer songs? I think this is the best approach.
As well, I think having this be an option that's disabled by default is the best compromise. This means it won't make any changes to the default state of the app which the majority of users are very close to), but allows interested people to use the feature.
Thanks for the great service, and have a great day!