When about two-thirds full, the burner is used to heat the air. With a striker similar to that used by welders to light their welding torches, or with an igniter. A Minimum of three, but preferably five or six, particularly if the wind is over 6 knots. A good ground crew can inflate in about 15 or 25 minutes and deflate, stow and be on its way in half an hour or less. It depends on how cold the air is and the size of the balloon.
Balloons lift better in cold air than in warm air.
The larger the air volume of the balloon, the more it can lift. Usually soon after sunrise or just before dusk. At these times the air is usually most stable and there is less wind to contend with. With stable air conditions you can fly any time during the day but this is very unlikely. As fast as the wind is blowing.