Mid-to late May is usually when they work best for me, when the new growth has begun to harden and leaves are fairly sturdy. Any sooner, and the cuttings wilt too easily; if you wait too late, they'll be too woody to root quickly. That having been said, my grandmother kept a barrel of wet sand out back and stuck in big (pencil diameter) branches whenever the mood struck. She got results, and it took a long time, but her starter plants were much larger than the ones I get from semi-ripe stem cuttings - I guess it's all a trade off.

Thanks for the info. My Carter's Sunburst camellia isn't big enough yet for pencil sized cuttings but a few tip cuttings might work.