How Do You Prove That You Worked X Amount of Hours?

I disagree, "johnny." I would not pay a bill from a doctor, lawyer, accountant, plumber, electrician, mechanic or other without some kind of itemization or description of work provided. And I wouldn't pay the bill without questioning charges I thought were inflated. I do this whether the contract is implied or actual.

And now, for a bit of shameless self-promotion: If you want a copy of the time & tasks worksheet I use (an excel file), PM me with an address to which I can send an attachment. I've recently revised my business management programs, am now only offering courses on request. Worksheets and tipsheets are free for the asking and once I revise the website will be downloadable from there, with a you-have-to-pay-for link to a walkthrough of each.