does turning off vBulletin for hours affect search engine ranking/indexing?

Okay this may be a silly question, but if you turn off vBulletin for a while (e.g., for a few hours for a major version upgrade) then won't all your pages have a "closed" message, and the Google crawler will see all your content for every page replaced with that closed message, right? So I guess what I'm asking is, could that have any effect on search engine indexing/ranking of your site?

Bump! For how long I can turn off VBSEO so it won't affect my site?

Spiders will report links as 404 errors but Google, Bin, etc., will keep trying for a reasonable length of time. Even up to 24-48 hours down time should be safe. Search engines recognize that sometimes servers crash and they'll make allowances for that.