I know my honeybees love the Magnolia, I have a big one in my backyard. The blooms are so large I have seen as many as six to ten bees to a bloom at one time. It appears they gather a lot of pollen from Magnolia.
My Hony Plants manual says some varieties produce a dark strong honey which resembles sorghum. For me the dark strong honey is my favorite. Had some for supper tonight! GOOD!

 

I have a small retail nursery where I propagate plants that good sources for bees. The Magnolia is one of the better sellers, as many beekeepers buy them to plant in thier landscapes. We sell a lot of Little Gem Magnolias, because they don't get as large as other cultivars. We also sell a lot of Tulip Poplar, Basswood, Sourwood, Willows and Harry Lauder Walking Stick shurbs to beekeepers. All these seem to bee good bee plants.

 

I have a 25 footer outside my bedroom window. The bees like it, its usually in full bloom on Easter, for about 2 weeks. The petals are attached very delicately though, so a bit of rain and some wind will blow them to the ground fast. Mine is protected by the house, but others I know about that aren't, generally only have flowers for a few days.