Norman says that 7pm is "seven bells." Later in the series, it is disclosed that Norm served in the US Coast Guard. As such, he should be aware that 7pm would equate to either 2 bells or 6 bells (depending on whether the ship split the dog watch). Character backstories are created as a series progresses. There is no way the writers could know in Season 1 that Norm was going to be in the Coast Guard later in the series. As such, this is not an error.
The calendar in the pool room reads 1982, and this episode aired in January 27, 1983.