Kerria japonica 'Pleniflora' pruning

Im after some pruning advice please for my Kerria japonica 'Pleniflora'. So far ive never pruned mine as im not sure how.

Ive read that is falls into pruning group 3, and needs a third of its stems cutting down to ground level each year. But when is the best time of the year to do this? Should it be done late spring after flowering to allow new growth this year?

Prune it back right after flowering. Cut all the stems that have flowered right back as hard as you like. Leave any younger stems as these will bear next year's flowers. 

Don't worry if it buckets down and you cannot get it done at the right time as it is impossible to kill so you can prune whenever you have time.  Mine has been hacked back at almost every season and in all weathers and still it fills the herges and spinney with glorious clour, not just in the spring either.  i swear some of it has been in flower for all of last year.

Thanks, I'll have a go at pruning it when its stopped flowering. So does it flower on the previous years growth?

Yes. that goes for all spring flowering and most early summer flowering shrubs. 

Thanks Gold1locks