[otrs] Time Closed Tickets

1 - A customer opens a ticket towards the tail “system”. 2 - An agent of the thing “system” takes in management the ticket, he resolves it and he closes it.ù 3 - Customer when he visualizes its ticket sees that the time associated to the ticket closed continues to increase instead remaining firm. Why the time does not remain firm? The time that I see in the window indicates the duration of the ticket when still it is not closed? Who can help me? Thanks, Ernesto.