1
general::
Phrase(s): till hell freezes over
Inf. forever. (Use caution with hell.) • That’s all right, boss; I can wait till hell freezes over for your answer. • I’ll be here till hell freezes over.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
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.
American Heritage Idioms