So, I finished my RDM AF3 and was testing the "Increases enhancing magic effect duration" on them. I thought at first it would be a 70% duration increase from 5/5 AF3 + cape. But after a few tests I found out the duration of my haste and refresh were 92.5% more than normal.
Here's a few screenshots I took of this extended duration:
Haste:
Start
End
180 * 1.925 = 346.5
Refresh:
Start
End
150 * 1.925 = 288.75
So I have concluded that the set bonus adds 22.5% time increase to enhancing magic duration if every piece really adds 10% duration.
Just wanted to contribute something for those RDMs that are planning on getting this AF3+2 set in the future. I am still doing more testing so if you have the set too don't be afraid to contribute! :)