Till a snapping turtle turns loose

I'm trying to find another expression that means a long but indefinate time - like the cows come home, but not this phrase

When pigs fly (this actually goes back to the middle Ages).
When hell freezes over.
It'll be a long, hot day in the middle of December when X.

Those mean an infinitely long wait, but "till the cows come home" is often used that way, too.

LONG TIME -- Coon's age; a month a Sundays, which is about seven months in duration; quite a spell; a long spell; since God knows when; a right smart spell; till a snapping turtle turns loose. From This Dog'll Really Hunt: An Entertaining Texas Dictionary by Wallace O. Chariton (Wordware Publishing, Piano, Texas, 1989, 1990)