Posted: 13/03/2016 at 08:27
I,would do it now, asap. Being so big you will need to prune your rhododendron quite hard. Forgoing the flowers for this year and moving now gives your plant more time to establish before the (hot) summer.
Those buds will prob not open for another 3 or 4 weeks ...too late to move then
Prepare your new bed and planting hole, trim any over long and damaged roots and water really well. Leave mound of soil around to create a moat and repeat watering for a week or two. Prune back the top.