Inquiry regarding the timing of IM7 issuance for bonded warehouses in France

The exporter is based in Korea, and we have a contract with a warehouse agent in France to store goods in a French bonded warehouse. I am reaching out because there is something I don't quite understand regarding customs clearance. I understand that a T-1 (transit document) is issued to transport goods from a French port to the bonded warehouse, but I don't understand the part about issuing an IM7 to store the goods in the bonded warehouse. A different warehouse partner I worked with in the past used to issue the IM7 only after 90 days of storage, so I am not sure which explanation is correct. I previously thought that goods were transported from the port to the warehouse via T-1 and remained in bonded status, and then an IM7 was issued after 90 days had passed since the T-1 was issued. I would like to know if this is correct, what exactly an IM7 is, and which agent's explanation is accurate.