This presses my buttons! No one needs to express and discard ('pump and dump' after they have had even a lot to drink - this just makes bf a difficult thing to do and stops it fitting in with what people want to do with their lives.
Here are the facts (courtesy of Medications and Mothers Milk by Dr Thomas Hale) - 'the bsolue amount of alcohol transferred into milk is generally low'. and further: 'maternal blood alcohol levels must attain 300mg/dl bfore significant side effects are reported in the infant.' Do the maths. Current drink driving limits are 80mg per 100 cl (which is 1 dl)...so in order for a baby to show significant side effects you need to have drunk more than three times the drink driving limit.
Any effects on the baby are temporary. Obviously it's not 'good' for a baby to have side effects, but they do go.....just as your liver processes alcohol and you are fine and alcohol-free later, so does the baby's. A tiny baby might be expected to handle this less well than an older one of four months (because of the immaturity of the liver).
Now, some people might not want any effects, or might not want any alcohol in the breastmilk at all....so they choose not to drink, or to drink moderately. That's their choice. Yes, think in terms of about two hours per unit, if you want to work out when your milk will be totally booze-free.
Use your own feelings as a guide, too. If you no longer feel drunk, then your milk has less alcohol.
Remember, too, the baby is drinking the alcohol diluted by your breastmilk. He then processes it in his gut. His own blood alcohol level will be way, way lower than yours.