Ideally, Gentoo should be mixed above 65 °F (18 °C).  Mix Gentoo for 120 minutes if between 65 °F and 75 °F (18 °C and 24 °C).  Mixing at temperatures above 75 °F (24 °C) may shorten the required mixing time to potentially as low as 90 minutes.  Mixing at temperatures below 65 °F (18 °C) may require mixing times of 3 hours or longer.