Eh, I wouldn't take any longer than 10 days on these things. I'm not sure if you're from NC or not, but for example, I have read that ECU gives a strict 10-day timeline from the time you receive your supplementary to the time you have to submit it. It just looks bad if you take longer and holds up your application.
And, the thing is that UNC's has been available since the 3rd. I had all of my stuff completely submitted by the 11th of June. You didn't really just "receive" it, as it has always been on their website--the e-mail they sent out was just a reminder for people who hadn't done it yet. I would try to finish it within a few days if you can.