"Have i missed the window?"

Most likely. The majority of popular herbicides/brush killers require the target plant to be in active growth to be effective. In late November and with temps in the 30's, active growth is no longer very plausible. You can certainly cut them back now but will probably just be wasting your time and the product if you apply now.

if the plant is dormant ... and not still sucking energy created when in leaf ... down into the root mass storage system ... then i would presume it wont suck killer down into the root mass ... but i never really figured out when that ends for the season... though i presume come ground freeze.. animation is suspended ... anyone have actual research on such??? .. and dont forget air temps arent as important as soil temps at root depth ...

that said.. if you want or need the exercise .. go out there and cut some stuff down .. and apply the root killer.. maybe it will work in spring maybe it wont.. when i was in doubt.. i used either spray paint or surveyors tape... and just marked the cuts to try to remember to check it all out after bud break ...

also... it will be easier to spray down a small sprout.. than some huge old vine .. which you probably wont get around to cutting until the releafs in spring anyway .. spraying and killing new leaves 2 or 3 times over summer. will eventually starve the root mass ...

btw ... just make the cuts.. and leave the vines hanging .. you really dont need to pull them down .. i actually harmed a few trees being to aggressive doing such ... or.. let them hang and dry for a season or two.. and they will pull out easier ...

ken

The weed killer is absorbed through the leaves so if there are not many leaves there might not be enough weed killer to do much to a large root mass.

I only use herbicide by applying a drop to a cut stem. It works when the timing is right. Hence my question. But thanks.

Here's a link for dormant season spraying and invasives control. The short answer is no, you should cut vines now but wait until new leaves grow before spraying, the long answer is it depends on what you're spraying.

https://extension.psu.edu/tis-the-season-winter-invasive-plant-control