as mentioned above, sometime timing belt cover is misaligned making some noise, it has some dowels for proper fitment,
yes, to avoid redoing all this work, mechanics make excuse that the sound will go away with time, infact it will be damaging some parts.
i think the timing adjuster/bearing is self adjusting, but still it needs to installed correctly, u can ask the guy patiently to fix the sound even if need to redo