Time is generally a guideline for me. It is better to have the brisket finish early, then having family or guess waiting around. If the brisket finishes early you can always FTC it. With a 10 lb. brisket, you could probably use a microwave (with the power off) instead of a cooler.
Primarily I always go by temperature, but texture is what determines when the brisket is done. Each cut can cook a little differently, so for example a brisket could be ready from the temperatures of 190°F to 205°F; or so. Many will take their brisket out of the smoker when the meat probe slides in an out like a hot knife through butter. But you don't want to overcook it, or it will just fall apart when cut. Begin testing for tenderness around the 190°F mark.
Also if you wrap, generally most will wrap when the brisket hits an internal temperature of 160°F to 165°F or so. But some times the bark doesn't get firm enough at that point, so I will hold off on wrapping until the bark sets.