a hypothetical time of day uttered in response to the question of "what time is it." when consumption of said malted beverage becomes an event that is either inevitable or required to proceed with life as we know it in modern society. No other time expression exists with beer in it, ie. there is no beer fifteen, or quarter to beer, there is also not a half past a beer or beer forty five. If it is not exactly beer thirty when someone asks you just say its getting close to beer thirty.
Half Past Time for a Beer...you're WAY overdue for a cold one and should've started drinking a while ago but weren't able to because you had to finish something up first. When you're finally to the point where you can actually sit down and enjoy a beer that you've earned or need, that's beer thirty.
In states where the liquor laws require that alcohol no longer be served after 2:30 a.m., beer thirty is the deadline by which alcohol much be purchased, lest the party come to a screeching halt.