A lot have to do with variety. The common impatient likes a nice shady
area. New Guinea impatiens like a lot more sun.

If it is still in its basket it could be that the plant is root bound
and drying out half way through the day. Water early in the morn and
then check the plant in the afternoon. If it is wilting water again.

If it is in the ground it could be that its feet are to wet. If this is
so just hold back the water for a few days and let it dry out a little.
Or could be that it is not getting quite enough water. The ground
should be damp a few inches below the surface.

Cut back the plant to a few inches and it should recover

Vicki