I can't say authoritatively but don't think they have specific hours. There really isn't anything to prevent you from going to the concierge sun deck so unless there is a net or something that they put over the hot tubs you'll be able to take a dip.
We were just on the Wish last week and know the Concierge lounge closed a 10pm each night. Assume that is when they close the hot tubs. Not sure if there is a way to access it besides going through the lounge? (We were usually out and about after 10pm so never tried!)
We sailed Concierge on the Wish in Sept. The lounge was still accessible after it's open hours the few times we wandered in not realizing the time, just not staffed. I was able to go out on the sundeck late at night but didn't notice if the hot tub was closed or not.
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