Should The URL Include a Date, or Not ?
A common URL pattern for a blog entry URL is Year/Month/DayOfMonth/Post_Name. This URL is generated at the blog entry creation time. It will never change anymore afterwards.
 Although it can be manually changed, it is usually discouraged
A common issue is that a blog entry takes time to be written, refined and then published. Therefore the date contained in the URL isn't the publication time. But since the publication time is the time the entry is created in the point of view of the public the date in the URL conveys only little meaning, just the time is took to create it.
Another point is that some blogger, i'm no exception, just create an entry to make a note. Theses entries are composed of bare notes without any relation or phrases. It serves as a unique receptacle of related raw ideas, useful not to loose them or to be obliged to scan through many medium just to make sure we didn't forget something that we thought important earlier. Then the date in the URL conveys very little meaning, mostly when we first had the idea about it.
On the opposite side, a date in the URL is quite interesting to know the relative age of a post without having to look in detail inside. This information is especially important in a technical field such as IT where the world is turning around quite fast.
We can see now that the timing information is important, just that the standard precision of one day is a bit overkill. All depends on the time taken to write the blog entry, and on the time scope it we be relevant.
For a article about a precise event, a precision of one day is interesting. At this end of the scale, blog entries that relates a event throughout a day would even have a hour precision. If most of the articles had a shift of 1 to 2 days in the creation time and the publication time, a precision of a day would be a fair deal. And the other side of the spectrum, an article about a slowing evolving subject such as demographic studies are fairly represented by a yearly url. For timeless subject such as philosophy, I still think that yearly would be adequate since one year represent quite a long time on a human scale.
Since usually my blog entries are in gestation for about 1 to 3 weeks, and are about IT subjects, a monthly precision is the most interesting since that conveys an adequate timing information in a changing world without having a false impression of exactitude.
Therefore I'm changing my URL format to a monthly rule, meanwhile allowing myself a different precision for special entries on specific subjects.
Unfortunatly it is very discouraged to change the URL once it's published since otherwise you have to redirect all the links that are currently pointing on it.
 from your other articles, from other blogs or from search engines