I have the one with the flat filter in it, which means that for black teas the brewing time is the 4-5 hours it takes to drink my tea. I usually use it for herbal teas because of this, but if I want black tea for later (because it truly does keep your tea super hot), I’ll make it in another container then pour it into this mug.
Sad thing is I forgot milky tea in mine, and I can’t get the smell off the rubber seals. I think it’s time for another baking soda soak, and maybe a vinegar or bleach soak as well. :/