I haven't yet been to Antelope Canyon, but I did spend nearly a week in late April, early May in Northern Arizona, southern Utah. The problem is that there are enough must-see places to spend weeks or months or longer. There are so many great places along the highway between Page and Kanab, Utah. The north rim of the Paria is great and if you are into some rigorous hiking, you can go part of the way down. You probably need a 4 wheel drive to get to the rim. The Paria canyon hikes are popular and require a far-in-advance reservation, but the north rim can be visited any time. A little farther along the road to Kanab is Wire Pass. You take a dirt road south about 10-15 miles (probably ok for a regular auto) and the trail head is on the left. A half day hike in and out will let you photograph a very nice slot canyon.
Whatever you do, I'm sure you won't go wrong. Have fun!