With the end of the world at Amara's hands fast approaching, Rowena MacLeod approached fellow witch Clea to be her second in using the spell to escape centuries into the past. After a brief argument, the two agreed on going to Greek Antiquity, specifically Crete.
However, before they could cast the spell, the witches were interrupted by Sam Winchester who brought them a needed ingredient in exchange for them hearing him out about helping to attack Amara. After believing that the plan had a chance of success, Clea threw her support behind helping to stop Amara rather than escaping into the past and was followed by a reluctant Rowena.
Most of the procedure is unknown, but it requires the power of two witches working together to work. The witches appear to have to agree on a single location in time they wish the spell to take them to. The known ingredients include an owl feather, yarrow root and the jaw of a pig.