I mean it's no less useful than a more precise, but less certain estimate. It means you either need to do some work to improve your certainty (e.g. in the case of this quiz, allow spending more than 10 minutes or allow research) or prepare for the possibility that it's 700 days.

Edit: And by the way given a large enough view, estimates like this can still be valuable, because when you add these estimates together the resulting probability distribution narrows considerably. e.g. at just 10 tasks of this size, you get a 95% CI of 245~460 per task. At 20, 225~430 per task.

Note that this is obviously reductive as there's no way an estimate of 5-700 would imply a normal distribution centred at 352.5, it would be more like a logarithmic distribution where the mean is around 10 days. And additionally, this treats each task as independent...i.e. one estimate being at the high end wouldn't mean another one would be as well.