is tkts booth at times square open on sundays? can we get aida tickets this way..or should we get ahead of time?

They are open every day, but there's no guarantee that Aida will be up.

The chances of getting tickets for Aida at TKTS on a Sunday depends, in part, on which Sunday you are talking about. For example, if it's a holiday weekend, like Easter, the chances are not the good.

There are many advance sale discounts for Aida. Check out broadwaybox.com, theatermania.com, playbill.com, and/or hitshowclub.com.

We were in NYC last Sunday to see Beauty and the Beast. I got our tickets by subscribing for free to Theatremania.com. They have discount codes you can use at ticketmaster. They do have blackout dates, so if you are not flexible, this might not be an option. Our Beauty and the Beast tickets were 35% off and we had great seats in the front mezzanine.