Is "last modified" time in XML Sitemaps important?

[ShaMenz]

My Tech lead is concerned that his use of a script to generate XML sitemaps for some client sites may be causing negative issues for those sites.

His concern centers around the fact that the script generates a sitemap which indicates that every URL page in the site was last modified at the exact same date and time. I have never heard anything to indicate that this might be a problem, but I do know that the sitemaps I generate for other client sites can choose server response or not.

What is the best way to generate the sitemap? Last mod from actual time modified, or all set at one date and time?

[AlanBleiweiss]

Glad to be of help Sha

[ShaMenz]

Thanks Alan,

I will continue to use the server response setting when generating other sitemaps and recommend that our Techs ditch the home grown script that assigns the single date and time in future.

II must say also, it is great to have such clear and reliable advice - very glad to have you around!

Thanks again.

[AlanBleiweiss]

Sitemap.xml files are one of many "hints" search engines use to evaluate, classify and otherwise associate relevance, importance and freshness of individual pages, and in turn, an entire site.

When the entire file flags every page with the same date/time it can have a negative impact, purely from the single-point signal perspective.  If the actual pages themselves have different date/time stamps at the HTML code level, those would counter the sitemap.xml file reporting, and either resolve it or just cause confusion.

Any time search engines have a potential conflict that needs to be resolved, the potential for less than maximum value exists.

Because of these combined potential problems, SEO best practices dictate that this issue be resolved, so as to ensure it does not, in fact, lead to problems, however minor they might be on a per-page basis.  If resolving the issue takes an extensive amount of time, an evaluation of how important the issue is to overall SEO.   At a certain point, you cross into the realm of diminishing returns.