It will take ages.
In reality, noone will even try to break that kind of encryption with simple bruteaforce attack. It is silly.
Today's encryption is mathematically almost impossible to break.
Problem is not with an encryption. Problem lays how it was implemented.
Nowadays, people don't break encryption with bruteaforce (maybe that do, but thats stupid

).
Actually most even don't break encryption itself.
As far as I know, most of the breaks are due to flaws on Implementation!
It is not a problem of encryption. Encryption is broken due to weak points of ways of Implementation of it or weak points of software that does it.
(I am not taking into account dictionary attack, keyloging because they are different subject)
I am not saying encryption is perfect or unbreakable. I am just saying that it is A LOT easier to find flaws on Implementation of it.
For example, it may take just 2 minutes If Microsoft has a back-door to Bitlocker... ( I am not trying to accuse them, it was just an example which was relevant to your case)