Is it safe to sous vide chicken to less than 74°C for a longer amount of time?
The USDA gives detailed guidance on time and temperature to kill salmonella. For cooking chicken at 60°C (which, to me, tastes undercooked) at a pessimistic level of fat, that's 35 minutes; at 65°C (tastier) it's 5.4 minutes. Note that these are holding temperatures: they refer to time once the target temperature has been reached, not from the beginning of cooking. And keep in mind that the chicken will never quite reach the temperature of the liquid it's in.