Yeah, it's something I can time myself: I'm on about 6 years of daily usage at this point so it comes very easily. Anki also lets you set a time-out on cards as well. I'll know just from looking at the front of the card whether or not I know the word. If I do, space then 'good'; if I don't, space then 'again'. Very rarely I'll know a card but only after a longer moment to think about it - that's a 'hard' card.