[[modified]] is a timestamp, and supports all the same formatting options as any of the date-related tags, for example:
[[modified|%I:%M %p]]
See the date tag related section of the using templates post.
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There’s no scripting support for accessing versions at this time. It’s been on the list for a while, but never prioritized it because no one has asked for it. I’ll see if I can get to that soon.