Landing & Takoff timings?

Hi everyone, Can anyone offer advice? I've noticed when watching my AI aircraft at airports that any aircraft arriving at the runway hold point for departure are told to wait due a plane on approach. This is obviously correct however the approching aircraft is sometimes 10nm out and in my view offers the departing aircraft plenty of time to be able to takeoff.My question is - Is there any way to change the distance timings whereby an aircraft is allowed to go while another is on approach? Is there any tool etc in FSTraffic or within avsim?Thank you in Advance :)