gran_orco said:

There will be a related errata question probably sent. The actual question does not in any way require FAQing and asking for it is a waste of precious FFG resources. The rules are very clear and very specific.

I have prepared a question about errata-ing the existing FAQ answer to ask if this answer should be edited to say " ...interrupt the OL at any time during his (the OL's) turn.. ."
If it is denied during back-and-forth then I will prepare another question directly about the guard-mimic issue.

This is just to eliminate the round-about loophole that poor rules-lawyers think can get them a wedge into an open and shut case.

OFFICIAL ANSWER FROM KEVIN WILSON:

Hi David,

I sent you an answer a week or two ago, but I guess it didn't reach you. Guard cannot be used against a mimic until the overlord's turn, so it cannot immediately attack.

-Kevin