Is it inadvisable to swim after acupuncture?

Yes. Some general guidelines including not swimming or bathing right after (few hours) acupuncture. I'm not aware of any studies - and there probably aren't any - about specific time periods. If you think about it, you just had a bunch of tiny holes punched in your skin, so i'd give it a day or two before you go swimming in a public pool or the ocean.
No. I advise my acupuncture patients not to engage in any strenuous exercise the day of treatment. The exercise can lead to a poorer outcome. Of the acupuncturists i know, the minimum time they use before returning to exercise is 4 hours to get full benefits of the treatment.