Very little alcoh gets into milk. Milk is made from blood, not from your stomach, so alcohol content of milk is linked to your blood alcohol level.
I can't search for a link right now, but there is research online(done by individuals, not the NHS) that estimates you can be 4x over the drink drive limit and still safely bf. Apparently your milk would have a similar abv to apple juice at this point.
The bigger risk (genuinely) is being unsafe to look after your baby.
You might get more help on the Infant Feeding board.
If you're having a glass of wine over dinner, then you don't need to wait.
If you're off out for the night and will be more than wobbly when you get home, then you will not be safe to look after the baby, so express before you go out and feed the following morning. You may also need to express whilst you're out if your boobs get too swollen and sore.
If it's your first time drinking in several months, remember that your tolerance will have dropped so don't do what I did on my first night out after pregnancy, I ended up blathered on half the amount I normally drink.
Levels of alcohol in breast milk are close to the level in the mother’s bloodstream. Levels will be at their highest between 30 and 60 minutes after drinking, or 90 minutes if you’ve been drinking with a meal. It takes two hours for one unit of alcohol (a small glass of wine, or half a pint of ordinary-strength beer) to leave a mother's blood .
The most common problem with alcohol is that it affects the let down reflex so the baby finds it harder to feed/may get agitated and dissatisfied. on average they take 20% less milk if you have had a drink...some babies may refuse
If you drink larger amounts it may affect the child's behaviour making him/her agitated and restless.
one reference:Julie A. Mennella, Gary K. Beauchamp. Beer, Breast Feeding, and Folklore.
i would suggest feeding your little one, have the drink soon after then leave at least 2 hours as the safest margin...or more if it was a large measure.