They need to first decide how long they plan to stay there, then compare any savings vs the cost of the refi. The closing costs could well make it not worth doing.
Next, we NEVER know what might happen (another Covid?), but the projection that the Fed gave is that they plan to continue lowering rates until 2026...we will probably NEVER see 2.5-2.75% again, but if the projections happen, we might see 3.5-4.5%. It will all depend on the economic strength, the job market and inflation. Soooo....rates are down about 1.25% from the highs in this bump. They project to go down another 0.5% by the end of the year....that doesn't mean mortgage rates will go down the full amount the Fed cuts, though. All in all, the bump from now through end of year will probably be a reduction of another 0.25-0.4%, IF the fed cuts them again in Nov/Dec.

Soooo, if your son can find a no or low cost refi, then it's a great idea to do it now since he's in the 7s....and he may even be able to refi again in 12-24 months....or he could hold off for 6-12 months and see if they get into the low 5s or better. Just like everything, there is risk and reward. No one can tell you what is going to happen, even the Fed Chairman. Based on this, I would suggest that if they see a rate that makes their payment significantly lower, and it doesn't have onerous origination fees and costs, then do it sooner than later....but if anyone could time the market perfectly, it's because they have a time machine. Since that's not possible, there is at best, educated guessing.