Set it once and never check it again. That way it will never go out of spec.
But really it would be fine even if you checked every 1000 hours. Stock, these engines can handle a ton of abuse and improper care. Taking good care of it would be checking every, say, 300 hours. If starting becomes an issue with either too much or too little compression, then it wouldn't hurt to check the lash. If it's too easy to turn the engine over, make the exhaust valve looser by maybe 0.002". If the engine gets too hard to turn over and/or it's kicking backward and ripping the cord out of your hand, make the exhaust lash a little tighter by maybe 0.002". These engines like about 0.006"-0.008" on the intake and 0.006"-0.010" on the exhaust. Adjust the exhaust to your liking (for starting) within that range.