Though the series never directly says, it likely takes in 1994. The reuinion pamphlets in Episode 1 read 'Class of 84'. Also, the paper miniatures set on the table, as well as the Game Masters screen, are all pre 1993. Later on in the series, references to movies and TV shows are made by the main characters that are all prior to the 90s.
The 20 sided die Lee brings to the party was modeled after the oldest D20 found in history; an Egyptian dice from sometime between 300 and 30 BC.