If the color is no longer clearish on the inside and it flakes it should be done.
One of my favorite dishes my wife makes -- and even I can make it -- is to take the shake, frozen or defrosted it doesn't matter, put on a foil sheet with a little oil, your favorite seasoning, some asparagus, garlic, onions and enoki on top. Then wrap them up individually, one for each person, and put on grill or air fryer. Takes about 10 minutes defrosted or about 25 minutes frozen. Served with shiro-gohan of course.