Forever, as in They said they'd go on searching till hell freezes over, but I'm sure they'll give up soon. This hyperbolic expression dates from the early 1900s. So does its antonym, not till hell freezes over, meaning “never,” as in I'm not giving in, not until hell freezes over.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
How to use till hell freezes over in a sentence
You've been living on the Union, and I suppose you think you can go on living on it till hell freezes over.The Lieutenant-Governor | Guy Wetmore Carryl
"I don't suppose we'll leave here till hell freezes over," said Meadville, who was doing up the last strap on his pack.Three Soldiers | John Dos Passos
Well, if they want to wait for me to be nasty to Tonet, they can wait till hell freezes over.Mayflower (Flor de mayo) | Vicente Blasco Ibez