That would be the worst consulting experience for the company and I think you can easily tell a different between a test and outsourced work.
Also that wouldn't likely save time. If the task will take someone 2h, I'd have to spend more than that: describing the task with all the relevant context, providing a mock of the environment it needs to be plugged into, reviewing the result, fixing any issues, changing it to match the internal style, and also waiting for the solution itself which may not even arrive any time soon. It's not like every (or even most) candidates will produce something you'd want to keep.
Even worse. A week long task without internal context or being able to chat with people who know it would be next to impossible to prepare. I've seen some projects which were thoroughly specced and handed over to a consulting agency. Half were not usable, the other half need heavy fixing. It was never a happy outcome.
Only if they've found a way to consistently defeat Brooks's Law -- and if they have, there are much more efficient ways to exploit it than counting on free labor of uncertain quality.
Also that wouldn't likely save time. If the task will take someone 2h, I'd have to spend more than that: describing the task with all the relevant context, providing a mock of the environment it needs to be plugged into, reviewing the result, fixing any issues, changing it to match the internal style, and also waiting for the solution itself which may not even arrive any time soon. It's not like every (or even most) candidates will produce something you'd want to keep.