Weed killer may be applied any time when the plant is in growth. Actually now is a good time as before long the plant will be withdrawing the sap into the roots for winter so it takes the weed killer down with it.
Just remember that translocatable weed killer (Glysophate) will affect anything with green leaves so take care when spraying that it does not drift on to desirable plants nearby.

Julia, this is what we used to do on the allotment:

Insert vertical bamboo canes close to the weed to encourage it to grow up the canes rather than smother plants. The stems can then either be left on the

cane and carefully spot-treated with glyphosate (eg. Roundup Fast Action or Job Done General Purpose Weedkiller) or untwined and laid on the bare soil or an adjacent pathway before being sprayed.

I also recall a chap on the allotment used to do this but he also placed a plastic bottle, both ends cut off, over the canes making it easier to keep the spray from the weedkiller just on the Bindweed. Good luck with eradicating it!

Yes, if you remove the cane the bindweed stem falls into the plastic cylinder and you can spray it without harming nearby plants. This works well if you catch and stake the bindweed when it emerges.
I have the same problem with bindweed,and once it has stealthily grown up through a plant and waves at you triumphantly from the top, you can't spray it at all! THat's when I try to find the stem and cut it off at the bottom. You can't pull the top growth out straightaway without decimating your precious plant but after a few days the weed loses its grip and comes away more easily.

I spray about now for the reasons OWD says. I have also been known to use a paint brush to apply it to those leaves 'waving' at me from the top of another plant.

my problem is that the neighbours just how it off next to our shared hedge, so it comes through to me too.

on the bright side we do sometimes get convolvulus hawk moths.

Our neighbour likes the pretty white flowers!

actually the flowers are pretty so I do understand your neighbour OWD.

Brilliant ideas all round! I’m fortunate in not having any bindweed in my garden, however I do have a mole. I wish I could persuade it to climb up a pole!! I squash the hills down, then it trundles back the same way & throws them up again. I bet he’s tired of collapsing roofs.☹️

Sadly the only way to get rid of a mole is to catch it.

I know Owdboggy but I’d rather not. Actually it has moved into my neighbours garden today, :-), she won’t try to catch it either.