From Antelope Canyon drive 124 miles, 2 hours and 15 minutes, to Monument Valley. You do not have time to go into the park so drive along highway 163 and pull over when you find a nice spot next to one of the monuments. There are several pullouts so don’t worry if you pass one.
This part of the journey is a lot of driving for the amount of time you spend at the monuments. It is nice to see them and you would have kicked yourself if drove all those miles and didn’t make it, but keep in mind that it is an extra 150 miles of driving instead of going from Antelope Canyon straight to the South Rim of the Grand Canyon.
Pro Tip: Get pictures from the North and South sides of the monuments on highway 163.