I know this is probably impossible, but we have been surprised before:

I want to search a Word document for *any text* that was added/edited after a certain date/time...

Come on geniuses... make my day....))

Word itself won't be tracking the timestamps of every edit (thankfully). However if you store your documents in a CM system (Sharepoint perhaps?) which allows version history then you will have made your own day

I can point you at a high-end system that does exactly this for government to track legislation but it isn't Word and isn't cheap.

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Andrew Lockton
Chrysalis Design, Melbourne Australia