It also says, "...he may, on extraordinary Occasions, convene both Houses, or either of them,..."I know there is no constitutional requirement to give the state of the union via a speech to the combined chambers. I don't think there is a requirement to give it each year. Doesn't it say from 'time to time'?
They have several recesses coming up in the near future, maybe he'll just keep them in session until they act.