It's not necessary to do the magnesium citrate before the olive oil/juice mixture. Check out the Classic Coke flush on the liver Flush FAQ s; that is where I got the idea from.
If you don't have bad gallbladder attacks, it's probably not absolutely necessary to be extra careful about dilating the bile ducts before flushing. Most complications come from people who have thousands upon thousands of stones, and very large stones, blocking their bile ducts.
There is no harm in taking the magnesium citrate after you flush. I have had no problems doing it that way, and have done 5 flushes that way.
A lot of people do their flushes this way. It's really not a big deal.