how long does it take for people to win by leaving a game?

sometimes it's a very long time, but sometimes it's as less as 10 sec
I don't get why it is random

I think it depends on how the computer evaluates the position. In an equal position, it takes half a minute or so. If it's clear you are winning, it only takes a few seconds.

I'm don't know whether a Stockfish analysis is done, or whether it's solely based on material advantage.

I think Lichess shortens the timer if the player left by closing the tab/app, and it's the standard timer for a disconnect in case their internet is having issues.

@George6W-obs my girlfriend tells me the same thing!

Stupid system. I played as black and waited 2 minutes first move of my white opponent. Score 1:0. I have never seen so much cheating in my chess life. Shame of you, semi-literate corrupters!

Forever & a Day ... You can't win by Leaving ,,, Unless ... While you have left your opponent Resigns

Akí korupční podvodníci spravujú túto úbohú stránku. Hanebné manipulácie.

i always thought it was based on the length of the game/how much time people have left on their clock