Is this an actual rule/policy in the NBA, though? I've never heard of this being implemented in the NBA. I know, however, that it exists in the NFL...
They can't hire an assistant until after his/her team's season ends, but I don't think there's a similar rule for interviewing. I think they can interview/talk to an assistant coach. They just can't officially offer a contract and hire them until after the season concludes.
I might be mistaken here, and will gladly allow a more knowledgeable individual to correct me...