I have a team of resources who complete projects, but their daily is interrupted by other tasks, phone calls, meetings etc.

Their standard daily hours are 7.5 hours, but I want to restrict their working time on a project to 6.5 hours to take into account interruptions.

I have currently done this by changing the working time, but, this affects the cost calculations, as they should be paid for all 7.5 even though only 6.5 are allocated to a project.

Is there a better way to do this? Should I be using the resoure available units?

Thanks

Paul