The step attribute is the step amount you can do in milliseconds, so in this case you should use 60 * 60 * 1000
(60 minutes * 60 seconds * 1000 milliseconds = 1 hour) as the value:
<input type="time" step="3600000" />
Note that this does not work in Safari, but I did test it in Chrome. Safari simply doesnt support this type at all, so no validation happens as far as I can see. Which makes this not universally compatible.