Like Samara's loyalty mission, this is a "no combat" mission, and as such provides substantial experience, cash, and other rewards with no risk - thus it's recommended that you undertake this mission as soon as convenient after you receive it. Note that, Garrus's loyalty mission is also on the Citadel and also requires talking to Captain Bailey, so showing up with Thane and Garrus in your squad can make for some efficiencies.