have you ever wondered what exact date of the events of reservoir dogs takes place? me too, and through a little bit of analysis, here's my conclusion:
at 33 minutes and 51 seconds in, you can see this calendar behind mr. blonde as he makes his first appearance after the robbery. given that the movie was filmed in 1991, if you assume this calendar is from that year and then match the month with the shape of the weeks to find all potential options, you're left with february 1991 as the perfect match.
now, given that they're listening to k-billy's super sounds of the 70s weekend, we can reasonably assume that this heist takes probably place over a weekend span of either friday, saturday, or sunday. in my opinion, friday should be ruled out because at 3 minutes and 15 seconds, mr. pink states that he was listening to the station "the other day." if the station only runs over the weekend, unless he's referring to the past weekend (which i choose to believe he's not), he probably would have just said "earlier today." also, if it was saturday and he heard the song on friday, he should've just said "yesterday." this leads me to believe the heist takes place on sunday, with my speculation also heightened by the fact that they're a bunch of guys in suits sitting around a diner for morning breakfast--a usual sight during a businesman's work week and before or after sunday church services, but not so much on an average saturday.
with all that as evidence, i believe the reservoir dogs heist took place on a sunday, with the date as either february 3rd, 10th, 17th, or 24th of 1991.