On average, how much time does it take to fight an opponent in a tournament? And how often do you need to play per week to avoid being excluded from the tournament?

It varies: from 2-3 hours to 10+10+n. This depends on many factors: the quality of the internet connection for both players, their tendency to restart or not restart, and the overall level of play ("skill") - there is a difference: on the 2nd week, someone might come with a decisive advantage (which strong players often do) or on the 3rd month:D... As for how many games per week, it depends on the rules of each specific tournament, but usually 1-2 games every 2 weeks is enough...