The time of day that signifies it's time to go outside and have a cigarette break (or alternatively, time to smoke a joint), usually taken at the bottom half of the hour.

To indicate to someone you wish to take a smoke break, you would typically peek your head in their office, and go "smoke thirty" to which you both hobble outside, have a cigarette and muse about how much you hate you fucking job.
Ben: Hey man, what time is it?
Dave: Ten til smoke thirty.
by cheeriomcmuffin April 5, 2009
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