A "professional day" is a term used in often in Consulting and on Wall Street to suggest the worker will not be working a traditional 9 to 5 job, but will rather be working 8 to 6, 8 to 8, 7 to 7, 8 to 11, or worse. Outright saying that the individual will be working 10 to 18 hours a day would be illegal in many circumstances, so the term "professional day" is used to convey such a situation during employment interviews
employee: (leaving the office ~7pm)
boss: where are you going?
employee: (cautiously) home
boss: (indignantly) we work a Professional Day here, get this work done