Yes. Replace the strings at least two weeks before your service appointment, which is about how long it takes a newly-strung harp to hold pitch reliably. There is some variation in that, but two weeks is usually safe.
I was also skeptical about timed-obsolescence for strings, until I changed mine at about two years last winter. (The rule of thumb I’ve heard is yearly replacement for professionals, every-other-year for hobbyists/amateurs.) It made a huge difference. You don’t necessarily hear the strings declining in quality because it happens so slowly, but you’ll immediately notice how much better they sound once you get the new ones up to pitch. Happy harping. 🙂