Interpleader

Hello
Help please understand the situation Interpleader.
There is a contract between the Seller and the Buyer. There is a third party - Payer who has paid the cost of the contract to the Seller for the Buyer on his (Buyer) behalf. Now Seller makes a discount on goods and must return part of the money paid. To bring them back to the Buyer, not the Payer, Seller offers procedure of Interpleader
How long under the laws of Canada may continue the trial?
Please tell if someone knows something.