Why is the 2nd timestamp seemingly before the first?

Fixed it! thank you for pointing it out, didn't realize that.

Joker Stairs Dance: https://scenestamps.com/scenestamp/01hv65eahhtfr58phx5keb1b1...

Timestamp :1:30:19 to 1:31:39

joker stair dance takes place between (starting from elevator)1:30:19 to 1:31:39(running from the cops where the dance ends) in the movie.

I meant where do the timestamp begin? Depending on the definition of "begin" you may have issues with different editions of the same movie.

I.e. if in the same episode Netflix adds it's own logo and Amazon doesn't, then 00:01:35 will point to different scenes depending if you're watching Netflix vs Amazon

You're definitely correct. Not even only on different streaming services. Movies have different cuts too. For instance, Blade Runner has 5 different cuts

It has to be more than 5 cuts, even.

you can mention those in the descriptions and the data can be updated whenever you like.

I think you've missed the point of the question. For many movies, there isn't a single canonical version as different editions are released for different markets.

There is an input for sharing streaming link while creating source. You are not forced to share but, it depends whatever is the timestamp on the streaming link you share