H. anomola subsp petiolaris has white lacecap flowers, which look slightly creamy on the plant.

Remove the old flowerheads now, just snip off the flowerhead itself. You don't need to do any other pruning at all unless you want to control the size or shape. If you need to control the size already then you probably bought the wrong plant :)

I remove my flowers around July/August normally, when I cut off the excess height from my ~35 year old plant. You do know how big it grows? I used to have it up to the eaves, and 20' wide, but as I get older and use a shorter ladder it is now only about 15' tall, but I filled a cubic yard sack with the offcuts, some an inch thick, a few days ago. As it gets larger keep it close to the wall by pruning or wind can pull the larger sections away from the wall. I expect to cut many growths, 2-3' long, off the top each year.
But the smell and the bees when it is flowering - superb.
Brian

Thanks for your advise Brian and Shrubs. So far it's just a junior and I hope it will thicken up to hide an ugly 10-15ft wall, which is why I chose it. So, I now undersand I have to keep it trimmed. Yes, the flowers are gorgeous, but 11 flowers in the first year is quite amazing as I thought it didn't flower for the first few years. Lucky me!

Sunflower you are lucky. I planted on on a north facing wall at about the same time as you, and so far I havn't seen a single flower. We got a good growth of foliage last summer, and it grew to about 5ft tall,but that was all. So far this year the plant has many leaf buds on it, so I am hopeful!