[dmg]

I've had my first nettle sting of the year- many more still to go 
The nettles are actively growing and the brambles buds are breaking.
Can I use glyphosate on them just now or wait a few weeks?

Dmg

[Trillium]

Glyphosate works only on actively growing greens, so you can spray the nettles now but don't bother with areas that haven't yet sprouted.

Nettles do make a very rich 'tea' so perhaps you could cut down the stalks and throw them into a bucket of  water to compost into tea.

[fatcat1955]

They make an excellent plant food too.

[Robster]

For reasons mentioned and including as an habitat for butterflies and as a decoy for cabbage whites i like to keep a patch of nettles.  But they do need to be kept in check.  After I cut them down last time I pulled up an enormous amount of root.  Very easy, extremely cathartic.  They'll grow back for sure but only the amount I want.

[mumofstig]

You have to wait for a dry day to use glyphosate - lucky you id you have any of those 

[Trillium]

They make an excellent plant food too.

  That was exactly my point.

[diospyros]

as an habitat for butterflies and as a decoy for cabbage whites i like to keep a patch of nettles.

Surely cabbage whites are only attracted to members of the cabbage family?  Do you see them round your nettles?  I'm  a bit wary of planting things that might attract butterflies in case I get accused of bringing in extra!