That's only if you're expecting a candidate to provide a perfect solution; and don't make it clear that the time limit should inform their design and not just m

That's only if you're expecting a candidate to provide a perfect solution; and don't make it clear that the time limit should inform their design and not just measure their speed of implementation. Part of software development is tailoring a solution to the scope of the problem, and this includes taking into account the time and effort available to come up with a solution. Someone who looks at that problem statement and designs something that will take a week has missed a very important requirement. You could reasonably scale up any problem to take an arbitrarily long amount of time, by adding onerous requirements (must have 7 9's of reliability). What I've found more rare and precious is the developer who can limit the scope so that items that are not up for negotiation like time (2 hours) & resources (1 developer) are respected. I fully expect a developer to state their assumptions up front, so that I can judge their design based on the stated assumptions and not some unstated imaginary assumptions. It also lets me see how or if they prioritize.