Quoted from Skyemont:
You guys with 30-70 people in the league is a lot. How long does it take for 1 league night of play?
This varies a ton on the format and the number of machines available, bottlenecking can be a problem.
The two 25-35 player leagues I'm involved with take 1.5-2.5 hours (mixed seed groups) for five games to about 3 hours (group based on seed) for four games.
If your scoring and groups are based on direct play and the better players end up in a few groups, that leads to longer playtimes. Playing the same games every week also results in people getting comfortable with the games and usually ends up taking longer.