by RainbowMoostache » Wed Sep 02, 2015 9:39 pm
If you mean as in when the heat bar (the red one) goes up, it does so in its own time. You'll simply have to wait, but once it reaches it limits, burning milkweed and such will be faster, so the waiting is much rewarded.
If you mean as in how to start a fire, craft a tinder drill and right click the fireplace. There's a chance for it to break though, so have atleast two with you to compensate for the other.