Timeline (Season 6)

NOTE:

• Days spent on each case include the day after they solve them, if it is shown in the episode.
• Day counts assume one driving day in cases when the boys hear about the case and must travel to the location, unless otherwise stated.
• Day counts count partial days as full days (meaning if an episode starts late at night, that night counts as a day)
• Priority of information sources: A)Dialogue, B)Logic, C)Art/Props Department, D)Other Official Sources, E)Conjecture.

IMPORTANT NOTE: The writers/crew at Supernatural decided to continue their tradition of dating things for the estimated release time of the episode, ignoring the fact that, because Dean lived with Lisa for a whole year between the end of Season 5 and the beginning of Season 6, Season 6 should start in 2011, not 2010.

According to 1st AD Kevin Parks:

They decided to do "soap opera time", because they didn't want to have to push the year forward for the rest of the show's run. So, just like in soap operas when people's kids are toddlers and then suddenly teenagers, so too can Sam and Dean spend a year apart while no time has actually passed in reality. (source)

If you want the timeline to be logical, just add one year to all dates except those that happened between Season 5 and Season 6.

2010/2011 - Between Season 5 and Season 6

Sometime in the 2010/2011 year - Sam has sex with a Hunter named Annie (7.19 Of Grave Importance)

Winter 2010 - Sam and Samuel hunt an Arachne in Bristol, Rhode Island. (6.13 Unforgiven)

Fall 2010 - Castiel refuses to follow Raphael’s orders and restart the apocalypse, leading to a civil war in heaven. Castiel makes an unholy alliance in order to be powerful enough to oppose Raphael. (6.20 The Man Who Would Be King)

• Season based on the fact that Dean is raking leaves when Castiel almost goes to him for help.

Spring 2011 - Sam and Samuel shoot a werewolf on the half-moon.(6.08 All Dogs Go to Heaven)