That's a camel's nose under the tent. If it goes unchallenged, there's no reason they can't come up with reasons to extend it to 6 months or a year.
So, instead of a 10-day waiting period for you to recover from your murderous rage, they could have you go through a 6-month in-patient anger therapy session each time you want to purchase a gun?
Yeah, I know, don't give them ideas...