This would do that. It matches what you specified, and using a Lua script line, adds a one-shot timer to fire after 112 seconds, that sends "exp1" to the command processor (thus, exp1 can be an alias).
See http://mushclient.com/pasting for how to paste that example into the client.
See http://www.gammon.com.au/scripts/doc.php?function=DoAfterSpecial for a description of DoAfterSpecial.
<triggers>
<trigger
enabled="y"
match="<hovering nearby> (Mythic) a green materia"
send_to="12"
sequence="100"
>
<send>DoAfterSpecial (112, "exp1", 10)</send>
</trigger>
</triggers>
See http://mushclient.com/pasting for how to paste that example into the client.
See http://www.gammon.com.au/scripts/doc.php?function=DoAfterSpecial for a description of DoAfterSpecial.