Need Help With a Goal

 I manage team of team of consultants in a software company. We are responsible for the implementation of our software systems at customer sites. I am looking for a goal which will help my team ensure that they are capturing all of the chargeable time and thereby maximising revenue for each contract.

The work carried out on-site is easy enough because they have to get a site-visit sheet signed by the customer which details the time spent there. It is the time in the office which is not so easy. Preparation, phone calls, email etc., the little bits of time which on their own are not significant but can add up. 

Any ideas would be appreciated.