Woody Thyme/margoram

[DaisyDiamond]

I have a bed of varieties of thyme and margoram/oregano which I bought as new plants this year. Previously I have found that my thyme in particular goes quite woody and doesn't then get much foliage on them the following year. They are in flower at the moment. When should I cut them back to avoid them getting too woody?

Any suggestions appreciated.

[Jerryfb]

Straight after flowering. Cut back so all flower buds are gone but not into the old wood