Meaning: waiting for something to take its own sweet time
Rewrite 1: until the leaves fall from the trees
Rewrite 2: until it’s covered in bureaucratic red tape
Rewrite 3: until the spots fall off a Dalmatian
Rewrite 4: after the paint dries and the bumpers rust
Comment: None. There are lots of things that take their own sweet time from which to choose.

More reading about clichés
What I found when I googled “clichés”:
• Phrases with Origins: “Clichés, phrases, one liners, sayings, similies, adages…”