(c) definitely only charge at full day granularity
(d) leave some slack in the accounting, favouring the client
The thing is that the client is not really paying you for your time, they are paying you for the value you can deliver. Time is a very rough analog, but so far seems the best that we can do and actually agree to.
So the above leaves the time-based accounting in place, but de-emphasises it as much as possible.
(a) charge a high rate
(b) preferably charge for projects or
(c) definitely only charge at full day granularity
(d) leave some slack in the accounting, favouring the client
The thing is that the client is not really paying you for your time, they are paying you for the value you can deliver. Time is a very rough analog, but so far seems the best that we can do and actually agree to.
So the above leaves the time-based accounting in place, but de-emphasises it as much as possible.