The most important thing is to make sure to check the official Times Guide for the exact date you are going to make sure the Resort Monorail line is running that early. I tend to use this link:
http://www.orlandoparksnews.com/p/weekly-walt-disney-world-times-guides.html
As you can see, the Resot Monorail start time varies by the day and these can/will change from week to week, so always make sure you look at the current time guide that covers your exact date. I trust the guide over any CM!
Assuming the Resort Monorail does in fact start running at 7AM on your Sunday in question (which as you see, did this past Sunday), then you're golden. I'd roughly budget a 15-20 minute trip from the TTC to CR, which will make stops at Poly, GF, and MK along the way. It should not be terribly long but sometimes you get the random "hold for further traffic clearance" that makes the loop longer than it should.
Hope that helps.