Hi mrritcher and welcome to TheSincairMethod!
A dose of Naltrexone will cover you for 12 hours, so if you're going to be drinking 12 hours after the first dose, redose in the 10th hour (and preferably wait an hour for that to kick in).
You may notice an immediate effect on your drinking, but it is possible to override the notion that you've had enough for the moment and enjoy getting smashed. The addicted part of your brain won't remember that you enjoyed getting smashed, but if you can pay closer attention and put the cork back in the bottle when your brain becomes a little indifferent to the next drink, so much the better.
Are you tracking your drinks? Here's a spreadsheet/graph combo you can use for that:
http://optionssavelives.freeforums.net/ ... graph-toolSo, I would generally suggest that you slow the pace of your drinking down if you can and when you feel like you could do without the next drink, act on that and switch to an AF beverage for the next little bit or even the rest of the night. Part of what we're doing here is to tease out the craving (which won't leave you alone) from just habitual drinking (you want another drink, but if you don't have it it's not a big issue).
Are you a daily drinker or do you binge?