How does "upvalue" work? Are the coins locked and for how l…

Upvalue sends satoshis directly to the author of the post. Locking lets you get the satoshis you committed to be locked back after a duration that you choose. Both options boost or repost someone's post, as far as I understand.

Thanks :-)

You're welcome!

when upvaluing your own messages sats reward treechat

also treechat makes 15% on each upvalue