the time at which parties normally start. it isn't an exact time, rather it refers to the time period between 9-11pm. This time can also vary regionally and by age group.
dude 1: hey do you know what time that bangin' party starts tonight?
dude 2: no they didn't say, so it's probably standard party time (spt)
dude 1: right on. let's go at 10:30