How long does the eounymus alatus take to grow to its full size, and how far apart should I be planting them?

In Britain the expected height and spread after five years is 4 feet by 5 feet wide, eventually reaching 8 feet. When you say how far apart should you be planting "them", am I to assume you're making some sort of hedge? If so, they'd need to be 18 inches to 2 feet apart.

Thanks Bamboo. I'll take your advice and plant the three plants 2 ft apart, and wait for autumn !!

Okay, but if you don't want a hedge as such, they need to be 3 feet apart minimum.