Most of our charges are made up by our hourly rate of machine with operator (fuel inclusive), beyond that we have some flat-rate charges for float fees and rentals (covered elsewhere).
So the question may be asked about some salient details concerning our practices for billing by time.
Very simply, we charge for all the time the operator is on the jobsite with the equipment - from the moment of arrival as he meets the customer and does a quick walk-through / overview of the site and tasks at hand, through unloading of equipment and commencing of operating it through the end of the day and quitting time or if it is a final day, after the equipment is loaded up and chained down ready to leave.
A small amount of time is expected to be spent by him communicating with our dispatch office by phone or text in order to advise them of his progress, and other scheduling details and vice versa (otherwise dispatch would never be able to coordinate bookings for him, meaning he would never have gotten to your site to take care of you had he not had a similar amount of communication days previously about coming to you while working on someone else's site).
If the operator stops the machine and takes a half-hour lunch, that time is not counted (most of our operators prefer to grab a bite and keep going, without stopping or deducting time, however).
He is entitiled to a mid-morning and mid-afternoon 10-minute or so coffee break without deducting for such, as is the case with any needed bathroom breaks.
A few minutes of machine maintenance (ie greasing) and refeulling periodically is also not time-deductible, however we try to tend to those things when there is a natural break in the action (waiting on supplies, bins, etc.).
We do not stop our time if there is such a stop for any reason on the site that is not of our making directly - such as a passing thunderstorm, another trade getting in the way, a delayed delivery of gravel, bin, or otherwise, holding up our progress, and so on.
Generally a machine breakdown is not time charged, but rather we will deduct the time it was broken until running again - unless the breakdown is directly jobsite-caused (as an example - getting a flat tire from a nail picked up off your site - we'll change or repair the tire on site, but not deduct the half hour it takes to get that done.
We bill a minimum charge each day our machine and an operator are on site (generally that is a 4-hour minimum), and we bill right to the quarter-hour, rounding forward to the next quarter. (So if we are on site for 5 hours and 40 minutes, we don't charge you 6 hours, but 5 and 3/4 hours.)