I always had a strong sense that most serious buyers are online, and therefore most lead registrations occur, within specific time windows. Given that general sense, I have always setup all of my own and my client's PPC campaigns accordingly. Now I have a year of organic only lead stats that prove the point. I tallied all of the past 12 months of my website's organic leads by hour of the day. The result is that 80% of all lead registrations occurred between noon and 11pm, a window that is about 45% of the day. Therefore, scheduling your AdWords campaigns to start at noon and stop at 11pm, allows you to time your AdWords spending to that peak consumer online period. This lets your competition spend some or all of their PPC budgets earlier in the day, before your campaign kicks in, thereby reducing your average cost per click. If you have a very small and limited PPC budget, you should focus your window even further, to start at 4pm and stop at midnight. That 8 hour window got 51% of all lead registrations.