[otrs] Solution Time of Tickets

Hi everyone!! I have a simple question: how can a modify the "Solution Time" of a Ticket. It's always set to 72h!!. When I create an email/phone ticket, the "Due Time" is set to 72h+current date. If a ticket is created automatically after a customer email, the Ticket also has a Solution Time of 72+current date...... Also, the SLAs don't affect to Solution Time...... so, how can I manage the Solution Time??? Thx in advance and have a nice weekend!