Hmmm...
The Pacific NorthWest is Rhody heaven, and we are Zone 7/8... I'm not sure there is a "Rhody bloom time", except that it is late Winter to Early Summer, as we have them that bloom from mid-March to early June. and it can depend on how the winter treated them and the variety planted... Cold wet winter/later bloom... I planted so that I have Rhody's blooming all Spring and early Summer...
Dave