The problem of NaOH (s) being hygrascopic and absorbing water from the air means that NaOH cannot be used as a primary standard because you can accurately measure out a sample but you can't know how much of it is NaOH and how much is water. This is usually not a problem with the solution. However, a solution of NaOH will absorb CO2 from the air and so its concentration will not remain constant. Whether the amount by which it changes is a significant problem depends on the intended use.
When using a standardised NaOH for titrations, best practice is to standardise it with a known solution of an acid prior to use. However, this is not essential if the time since it was last standardised is short. If it has sat unused for a week, I'd probably re-standardise. Overnight is probably not a problem.