How does this work?

When do you pay both the big and the small blind?

If you sit out for a whole orbit, then come back in and you're not in the blinds. We treat it like you're rejoining after missing a full round.

If you sit down before the big blind and decide to join, you'll need to pay only the big blind, as this is your first hand.

To avoid paying both, sit in when you're ready to play before a full orbit passes.