If your exercise truly takes 1 hour, and you're evaluating it on the basis of 1 hours' worth of effort, then fair enough. I would say that roughly equates to the technical phone screen in this case, except without all the annoying "let's talk about every little thing we're doing while we're doing it, so it takes twice as long" BS.
And there's nothing wrong with whiteboarding, if done appropriately. Whiteboarding a system design question is totally appropriate. Asking a candidate to write down code for finding the longest palindromic substring of an input string in linear time is not. I've never come to a situation where writing anything more than the barest pseudocode outline for what to do on a whiteboard was the best way to get a real world task accomplished.
And there's nothing wrong with whiteboarding, if done appropriately. Whiteboarding a system design question is totally appropriate. Asking a candidate to write down code for finding the longest palindromic substring of an input string in linear time is not. I've never come to a situation where writing anything more than the barest pseudocode outline for what to do on a whiteboard was the best way to get a real world task accomplished.