As the new ausf G was only produced from April 42 on, this would have been the first planned German offensive that could've used them.
So 22nd pz div, may 8th,= first mass use?
The above photo from bundesarchiv, via Wikipedia article Battle of the Kerch Peninsula, shows an early G in crimea in may 42. It has early features: the smoke candle Armored cover on the top left of rear-plate; and globular muzzle brake. The large white tank numbers and spotty camo are consistent with 22nd pz; there's a pic of another identically camo'd G in the Repairing the Panzers books, which was confirmed as 22nd Pz Div by Craig Ellis.
First use of long 7.5cm Pz. IV G : I recall, dimly, once reading that the first examples were sent to the crimea to take part in Manstein's 8th May offensive, Unternehmen Trappenjagd, which recaptured Kerch and wrecked 3 whole Soviet armies.