Excel 2007 has a problem with time as an axis in charts. Using ‘the decimal version of time’ is probably the best workaround.  

The Microsoft blog you refer to closes with:  


  “In summary, whenever you need to create a time series chart where the units are smaller than a day, avoid using line, column, bar, or area chart types. Instead use an XY (Scatter) chart to accurately reflect the span of time.”  


but even so the example used there requires decimal versions.  

As mentioned by @Neal, this has been fixed for Excel 2010, as indicated by Microsoft would be the case. 

Your question also mentions “days since some arbitrary earlier date”. This is a date matter for which no workaround is required when considering whole days. Formatting the source data in date format should be sufficient.

Using a time to set XY chart axis scaling as in Excel 2003
I have a web application that uses the left navigation for major functionality and tabs for displaying different information within a function. One function is to enroll in something. There are several steps, with the last step displaying a summary of your selections before you submit. (All data selected during this process needs to be shown here before you click on the Submit button.) What is the best way to display all data if tabs are already used for the steps? More tabs or using an accordion and showing one or two sections expanded and the other sections collapsed or something else?
