I've bid hundreds of jobs and also done many T&M ones too. What the customer sees from your billing, in my humble opinion, is too much information. Just like the sales process should not include too much info, neither should the bill. You do need to document for your own records the exact times that the installers left the shop, arrived on the JS, took lunch breaks...etc, but you do not need to let the customer know this either, unless requested on a T&M bid by the customer. If you arm the customer with too much info, they will become a dangerous adversary instead of an excellent customer reference. Be careful in disclosing too much information. You will also end up losing money over the long run for your net, net. If you estimate a job to be 21.5 hours and the job goes smoother than expected, you may usually bill somewhere close to that to make up for those jobs that go over on contract or for troubleshooting problems. Remember, you are in business to service the customers needs AND to make money/a living. Be fair for both you and your customers and you will be just fine.

Mike