Fuel tanks are switched approximately each hour. Fuel tanks are ALWAYS
switched overhead or in close proximity to an enroute airport.

Tony wrote:
About fuel management --for what it's worth I liked to taxi out on one
tank, switch over to the take-off tank for run-up -- I'd break the hand
of anyone who tried to switch tanks afterrunup and before takeoff!--. I
figured at that point I proved both tanks would run the engine. I'd fly
away half the tank I took off on, switch over, and take most of the
fuel off the other tank. One of the thought processes was that the
first tank still had enough in it to get me back to where I started
from when I switched. (East coast based, nearly all first legs were
into a headwind). No matter what my flight plan said, when I switched
back to the takeoff tank (now I had somewhat more than 25% of the fuel
left) I was going to land for gas.