Till the cows come home
Definition 1 of 1
Pro Tip 1/3Rural Origin
The phrase comes from rural life where cows return home in the evening, suggesting a lengthy duration. 
He could practice his guitar till the cows come home and still enjoy it.
Pro Tip 2/3Indefinite Duration
'Till the cows come home' indicates an indefinite, possibly excessive, amount of time. 
You can wait for a perfect opportunity till the cows come home, or you can seize the day now.
Pro Tip 3/3Hyperbolic Expression
The phrase is often used to exaggerate, suggesting someone is doing something longer than necessary. 
She can complain about the weather till the cows come home, but it won't change anything.