As Siddharth Shah noted on Search Engine Land, it’s a tricky balance. Spend too much too soon and you might suffer a lower ROI and not have money left for Cyber Monday. Spend less and you might be missing out on consumer volume, he observed. Crunching the numbers for the days surrounding Black Friday (the day after Thanksgiving in the US) and Cyber Monday (the first workday after the Thanksgiving holiday) can prove quite enlightening. It turns out there’s a tempo to the spending. Holiday shoppers hold back on the week leading up to Black Friday, and then spike on Black Friday. They hit anoth…