Adriano, the MATAF daily summary that I sent you places Nicholson's Ju 88 claim at "T-1968" which is bT1968 on France Lambert Zone 3 grid. This translates to 43° 46' 46'' N, 5° 03' 30'' E, a point on the banks of the River Durance, 2.75 km SE of the centre of Orgon (Bouches-du-Rhône) and about 125 km south of Valence aerodrome. That's a distance that a P-51 could cover in about 20 minutes at cruising speed.
Frank's MTO list times Nicholson's claim at 0925–1230 (which is, I guess, local time = GMT+2).
ULTRA CX/MSS/T281/39 (file TNA HW 5/566) says:
From KABEK ((KG)) 26 on 18/8:
Low level attack by 4 Mustangs on Valence at 0607/18/8. 1 Ju 88 total loss, 1 gantry crane (total loss. casualties – nil.
NOTE: The time in that message is GMT.