How do you document or proof the hours you were coding when on an hourly paid freelance job?
I normally use timesheets for in-house consulting, but if a customer would question the billed hours that I was working on my own in my office, I couldn't proof anything.
Is there some typical contract clause that you can use to safeguard against having to be able to legally prove (witness or similar) the duration, as long as the billed hours are resonable and documented in some basic form?
You need to look at this issue from another perspective - the mutual trust.
There is no way to prove the number of hours you bill your client is the actual number of hours you spend on the task you are assigned.
Before you take the task, you should ask the client how many hours they expect you to spend for that task. Then you tell them how many hours you will need. You and your client eventually reach a mutually acceptable number of hours needed before you start the task.
You go do that task, document the hours you spend in a readable format. After you finish the task, report the result back to the client and then bill them with the invoice and the time sheet.
If the number of hours is within the reasonable range, say you told them you need 40 hours to do the task and you put in 42 hours, chances are the bill would be accepted. If you report 50 hours, 25% more than expected. Yes, they would question you. And you expect that. So, you would have to explain why you spend 25% more than what you agreed earlier.
If you did all that and the client still give you hard time by asking you to provide proof of time spent. You and your client are having the mutual trust issue. This is another problem, not what you're asking in this question.
If you’re working as a freelancer there are legit sites that handle invoicing automatically to bill clients for hours of work. There are also lots of time tracking tools online that you could use to track work hours. However, there are different approaches to time tracking like Time Doctor, which tracks time accurately on real time. It gives you analytics of your workday on where exactly you've spend your time and how much of that time is productive or unproductive. Another time tracking tool is Toggl, which automatically syncs with Quickbooks and Freshbooks (accounting tools). It also gives you record of work hours through mobile.
Generally speaking all that is required is a log of your activity, anything that you can refer back to at the end of the week to submit your hourly billing.
Any documentation would be helpful if the client questioned your invoice or refused to pay for all of the hours you billed. The lack of that documentation would pretty much turn it in to a 'he said, she said' battle, while the documentation itself, for the most part would be considered reasonable proof if challenged in court.
A few suggestions that you may find helpful:
