I use ring stakes that they grow through. so yes put the stakes in place when they are about 6-10" tall so you can see where they are and if you are using a single stake tie the stems in regularly.

Thanks for coming back, I must admit I put stakes in last year but far to late as I did not realise how tall they would grow. As you both say I will get the stakes in much earlier this year.

I don't like those nets, I prefer using a tomato cage. I'll usually invert it upside down, but it works, keeps the flowers upright even in torrential downpour and you can cut them for an indoor display without that net in the way.