Earlier quoted context omitted.
The trick is to do these sort of engagements as a fixed price contract. You could have probably done an assessment in a hour or two. Then you charge on what you estimate is the value to the company.
I should have, but it would have been obvious that I pulled a fast one on them as the fix was really quite simple. Instead of building a Hadoop cluster I replace a sql sub query with a bitmask. It really only took an hour to figure it out but they let me charge the whole day.
Also, can you describe the problem? It sounds interesting.