Average length of a game? How do you even know length of a game?

1 - looks like PGN doesn't include both the start and end times of a game, but somehow you can search games by duration eg

https://lichess.org/@/nicbentulan2/search?durationMin=600&durationMax=900&mode=1&players.a=nicbentulan2&sort.field=d&sort.order=desc

guess the midpoint (or greater end point for a more conservative estimate) of each interval and multiply by number of games but is there anything better?

2 - if the PGN doesn't include both then how does the system know the duration? (so it knows but doesn't tell us in the PGN?)

3 - is there a way to tell from the insights the average length of my games?

I guess I can't just do average number of moves times average time per move because that assumes uncorrelatedness.

@TheKingClash said in #2:

lichess.org/insights/nicbentulan2/nbMoves/variant

oh yeah that's length in moves but not length in time

As for 2016, the average length of a chess game was 39 moves. But a chessboard was probably 39 cm.

30 - 35 I guess