In the Netherlands league season is from September to February/March. Most, if not all matches are played on the weekend, on Saturday or Sunday. And the groups in the league are usually 8 teams or more (note that I left in 2016, so before covid and everything), so you have a match almost every weekend outside of holidays. This means that if you are a tournament organiser and you want players to show up, you will schedule your tournament from March onward. So from March to June is tournament season.
Although there are notable tournaments just before the start of the season in early September and during the christmas holiday, between chrismas and the new year if you can believe it. Those usually had the best atmosphere, because everyone showed up, whereas during the tournament season people might pick and choose.
Most clubs close for the summer, but most clubs have individual members that organise replacement sessions. But these are not club sessions.