What is the amount of zakat due on money saved through "jam'iyyat" (cooperative societies) that will be spent entirely over several months for marriage expenses?

You must endeavor to determine the amount of money in each year, and whether it reached the nisab (threshold) and a hawl (full lunar year) passed over it. If this is established, then zakat for the past years becomes obligatory upon you, because zakat is a right due to others and is not forfeited by the passage of time.

However, if the amount falls below the nisab during the hawl, then no zakat is due from you, and you begin a new hawl when the nisab is reached again.

The estimated nisab is the equivalent of 85 grams of gold or 595 grams of silver.