I have submitted a resource called XenIco and few hours later added screenshot and updated new version of the resource. Now in the Information block in the sidebar, first release and last updated times are showing the same while under version history tab the times are correct.
You need to post a new update message for that time to change. Normally, when doing a release, you'd have an announcement with it of some sort.
As this is basically intentional, though I appreciate that it's not 100% intuitive. The alternative potentially has people hunting down update info in multiple places to figure out why it changed: now it's just when you post an "update" (distinct from a "version" as an update doesn't have to be a new release).