Make a trigger, and then "group" the unit in question to the trigger.
Open up the trigger, and now you should have new 'activation' options:
vehicle - trigger activated by the person grouped to the trigger
whole group - activated only by EVERYONE in the person's group who is grouped to the trigger
any member of group - activated by ANYONE in the person's group
I think that's it. Set it to "vehicle", and then click "not present". Now select 'timeout' like HateR_Kint said, and set the time to 10/10/10. However, leave the 'condition' field as "this". "Timeout" means exactly what you want: once the trigger is activated, after 10 seconds, if the trigger is still activated, the trigger will fire. "Countdown" means that once the trigger is activated, after 10 seconds the trigger will fire, regardless of whether or not it is still activated.