Hello. Everybody will have their own opinions on wether you should check the valve clearances or not.
At 25000 mine where all in specification, no adjustments required. I think most people get this result at that mileage. Other foccers will confirm if this is the case.
Waiting an extra 1000 miles before you check them in my opinion won’t be a problem.
Understandably your mechanic may be non commital, he hasn’t got a crystal ball, he won’t want the comeback on him if anything should go wrong.