West Coast,
All depends on the mark of Lightning. The F2A (used in Germany) had only fuel in the belly tank the canons were integral. It could do up to 1hr 15m at low level (its primary role) and up to 1hr 55m at high level. Obviously no targets attacked. I have a 10 minute flight in my log book flying an F3 Lightning, with both practice missiles expended against 2 Jaguars. This was a short range airfield defence mission. as soon as missiles were expended you had to land ASAP to refuel and (practice) rearm.