Definitely, even with heavy kava, you should still plan on sleeping about an hour after consuming the kava.
Two things you should note:
1. You might have "reverse tolerance" (RT). This means that in the beginning that you will need more kava than you will after a couple weeks. Some people don't feel the full kava experience the first time, or even in the first week, though if I had to guess I would say that the average person with RT would probably take around 3-7 days to "break through" the reverse tolerance and feel the same effect from the same amount of kava.
Also, or course,
according to kavadude's census, around 2/3 of people experience this, and 1/3 don't.
If you do, the length really just depends on you, how much kava you use, how frequently, and how well you prepare your kava. I personally think that a lot of "RT" is due to newer people not knowing how to prepare kava the correct way, though there is a very real possibility that "RT" does still exist but if you do indeed feel it, it isn't the end to your kava experience.
Just continue to consume "as much" kava as possible (not too much of course, but more than, say, 1 tablespoon) every single night and you will gradually feel the effects more and more from the same amount of kava and then there will be a point where you "break through" and really feel the full effect from a given amount of kava.
2. Also based on
kavadude's census results, the average amount of kava per "session" seems to be between 4-8 tablespoons of kava, just so you have a ballpark. Of couurse, like Gradius said, you might need only a small amount because there are also those "lightweights" like Vekta that only need 2 tablespoons to feel a significant effect and you will feel the "medicinal" effects from a lower amount than most use. On average, assume that 1tbsp weighs around 7 grams.
Hope that helps. Let us know if you have any other questions.