German to English Other Human Resources Contract for IT support

I just can't think of a snappy translation for this. Basically this is a contract between two entities, one of whom will be providing IT support on behalf of the other. The appendices of the contract specify all manner of details regarding the collaboration, one of which is the manner in which the second party should react when they have been assigned an IT support job.

"Einsatzzeit" relates to the amount of time a technician is out on a job, from start to finish, and which is billed at the end of the month.

Has anybody come across a nice phrase for this?

Thanks in advance