The vast majority (four fifths) of Bomber Command sorties were at night, almost no daylight missions were flown from January 1940 to June 1944. Once daylight missions resumed with the invasion of France many of them were aimed at targets in Normandy to support the army, daylight attacks were made on Germany after that but not directly in conjunction with B-17s as far as I'm aware. The two air forces used quite different techniques, Bomber Command flying a much looser 'gaggle' formation even during daylight than the tight 8th Air Force 'combat box'. If the 8th Air Force and Bomber Command attacked the same target it was typically by day and night respectively, though when USAAF B-17s made daylight attacks on Hamburg in July 1943 following RAF night raids they found dense smoke from the previous attacks made targeting difficult and generally avoided combined attacks after that.

A single Bomber Command squadron briefly operated B-17s (as the Fortress I in RAF nomenclature). From July to September 1941 (prior to the introduction of the Lancaster, so the types didn't fly together) 90 Squadron made daylight attacks with small numbers of Fortresses but with little success; from that point RAF Fortresses were flown by Coastal Command rather than Bomber Command until 1944. In that year 100 Group, Bomber Command's electronic warfare specialists, employed Fortress IIIs as RCM (Radio Counter Measures) aircraft, flying at night to jam German radar. USAAF B-17s had also, briefly, flown night bombing raids over Germany with the RAF; between two and five B-17s of the 422nd Bomb Squadron took part in raids on Hannover, Mannheim, Munich and Frankfurt in September and October 1943 flying alongside RAF types including Lancasters.

So a small number of US B-17s took part in night attacks with Lancasters, and RCM Fortresses gave jamming support, but there are no joint day missions that I can find in Middlebrook & Everitt's The Bomber Command War Diaries.