This question has been asked many times. In brief, pruning azaleas and rhododendrons in early March will remove any flower buds for this year. For this reason alone, the best time would be after flowering and just before new growth commences. Nearly all azaleas will respond well to pruning by 1/3. Rhododendrons vary by variety and will, in general, take longer to recover enough to produce flower buds again.

zooba, mainegrower has given you good advice. You really have nothing to gain by pruning before bloom, better would be immediately as flowering has finished.

And if you aren't familiar with the growth habits or pruning procedures,

Azaleas have growth buds all along their stems under the bark and will sprout from just below any cut you make.

Rhododendrons have dormant growth buds in the leaf axils (where leaf joins stems). Make your cuts just above a rosette of leaves and new growth will emerge from the dormant eyes there. If you have to cut into a branch below any leaf rosettes, look for faint rings in the bark where there once were leaves - close inspection should reveal small bumps, those are the dormant buds where there once were leaves and cutting just above the rings/bumps should stimulate the dormant buds into growth. If you can't find the rings - make your cuts where you must, then go back when growth emerges and remove any bare stubs that remain above...

Sorry for the late reply. Thanks for the advice. I'm not sure if you agree, but I've read several articles that suggest the best time to do heavy pruning is actually early spring, but you will sacrifice the flowers for that year.

I'm willing to forgo the flowers this year to ensure that the plant remains healthy. Thanks

I'm not sure of the reasoning behind the advice you've read about sacrificing a year's bloom by pruning in early spring. The fact is that azaleas to a degree and rhododendons to greater degree naturally put on their first - and perhaps only - surge of growth after blooming. I can think of no reason why any advantage would be gained by pruning prior to bloom time. In fact, the possibility of soft new growth stimulated by the early pruning being hit by a late frost constitutes a distinct disadvantage.

According to the research I have done on Azaleas and pruning is that you ought prune after the bloom to ensure a bloom both the current season and the next season as the responses have said thus far. This is due to the blooms come from buds that develop on the previous season growth.

However...

If you are looking to do a VERY serious prune job (aka cut back to ~12-18inches... yes that is VERY small) Walter Reeves advises doing it before the bloom, and specifically Late February - Mid March, as it is in the best interest for the health of the plant. As a trade off you will obviously not have a blooming Azalea that year. Because Walter's advice comes from zone 7&8 and the original poster and question is from zone 7 it is something to consider.

Here's a link to Walter's webpage and Shrub Pruning Calendar: http://www.walterreeves.com/landscaping/shrub-pruning-calendar/

Zooba72 will be fine waiting until after bloom to prune, even if not interested in the flowering, will then be past the possibility of a late winter or early spring freeze. Damage from freezing is typically greatest close to pruning cuts, by waiting he/she eliminates that risk.

Azaleas will begin to sprout from heavy pruning in short order. Dormant buds on rhododendrons will begin to grow within about a month on smaller stems, 8-10 weeks on taller main stems - giving plenty of time if pruning later in Spring for growth to form, mature and harden off before next Fall's weather change again.