When does the Bengali bride start carrying the gachkouto?

Generally, After the morning bath and before or during the puja rituals. The bride usually takes a ceremonial bath in the morning (often after the Gaye Holud, if it’s held the day before or earlier that morning). Then she performs puja at home, often to the family deity or at the Tulsi plant.

The gachkouto is usually introduced at this point, especially it holds symbolic items like sindoor, coin, used during these early rituals.