The past tense of have one's nose to grindstone is had one's nose to grindstone.

The third-person singular simple present indicative form of have one's nose to grindstone is has one's nose to grindstone.

The present participle of have one's nose to grindstone is having one's nose to grindstone.

The past participle of have one's nose to grindstone is had one's nose to grindstone.