Folk have been setting dates on the Rapture for a long time. If you check the inerrant internet repository of all knowledge, you’ll find dates set for March 21, 1844, 1914, 1981, 1988, 1994 (Harold Camping’s first date), 2011 (Harold Camping’s second date), and even 2060 (Isaac Newton).
But this is only recent history. Before the Bible was even finished we had people saying that Christ would return—in fact, the second letter of 2 Thessalonians was because there was a teaching that the Day of the Lord had already occurred (2 Thes 2:1-2); Paul actually kicked some folk out of church for teaching that sort of thing (2 Tim 2:16-18). Some sites online have even tried to record the history of date-setting, though it’s definitely not comprehensive.