Hi Useless ;-)
I don't know that there 'is' a right or wrong time to plant it, i've planted this plant at all times of the year.
I'll be interested to hear what others say.

So long as you keep it from drying out( but don't over water) planting now will be fine. As louise says you can plant Aubretia at pretty well any time. Most pot grown hardy perennials or shrubs can be planted antime when there is no frost in the ground but the ideal time is early autumn or spring.Autumn is particularly good as they won't need much watering and will settle in over winter and grow away strongly in spring .