Part 135 duty day is 14 hours. Are you part of a scheduled or nonscheduled operation? Is it nonscheduled/continuous on call? If so, then it is up to you to decide when duty starts. Transportation that is "local in nature" can still be part of your rest. Therefore, if you have a 2 hour call out, you do not necessarily have to start duty when you are called. I believe that it is your discretion.