It depends on the crowd level and where you are in the rope drop throng, and also, which route you take. We tried it during spring break last year, took what I now know is the long route (straight through the castle), and even though we were at the very front of the pack, next to the CMs with ropes, 7DMT had a 40+ minute wait when we were allowed over. That was a busy (but not mega-crowded) period last year, though, & 7DMT was a bit newer then.
Here is a link to an article I read about the lesser-known "short route" to take when heading to 7DMT at rope drop:
http://www.easywdw.com/easy/blog/mi...er-bell-moves-the-4th-fp-magic-kingdom-52814/
Keep in mind that the article came out 2 years ago, so YMMV.