Unfortunately, there is no specific statement from any governing body stating how long remedial/rectification works should take. It’s more than likely that your contract might mention ‘reasonable time’ but how do you measure this? What is reasonable time? Weeks? Months? Longer?
If you find you have been waiting for far too long for your snagging issues to be rectified, you can always contact your warranty provider advising relations between yourself and the developer have failed, and you feel the contract terms are not being followed.
Good luck!