Chasidish Yeshivos that are closed during Tishri don’t have summer vacation, so it sort of equals out. The zman starts about Rosh Chodesh Cheshvon, give or take a few days depending on the Yeshiva. Some Yeshivas do try to start earlier to avoid such a long break – it’s not cast in stone.
Supposedly the idea is based on the timeline of the pre-war European Yeshivas when it took the Bochurim days of travel to reach home for Yom Yov, and days again to travel back after Yom Tov.
Although many are against so much time off, it’s generally useful for most households, as it’s a busy time, with setting up the Sukkah, and dismantling it afterwards and other Yom Tov related chores where bochurim can be handy and learn to help out around the house…
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