If comfrey tea is at all like compost tea (and in this aspect, I believe so), you don't want to wait for anaerobic bacteria to get going in it. They're often toxic to your garden plants. So make your tea, let the water cool, and use it immediately.
Compost tea lets you multiply the soil- and plant-helpful organisms you've already got going in your compost--as long as you keep your compost tea aerated (even by vigorous messy stirring several times a day), and feed the microbes a little (something sugary, like molasses; even flat Coke would work), and use within 24 to 48 hours--while your microbes are at a peak, before the anaerobic bacteria move in and take over. Apply it very gently, so as not to break up the larger, more delicate protozoa and such.
Thank you for adding this information. The sources I found all referred to the long- steeped tea.
Many visitors to our Soil and Composting Forum have also not seen this information about compost teas. So many sources originated years ago and called for long brewed teas; other wirtings carry that forward.. Recent information, as you have explained well, call for teas that are highly aerated, and used while fresh and full of good mocroorganisms.