With invasion support and V weapons strikes Bomber Command was doing quite a lot of daylight raids from 14 June 1944 onwards, then hit Germany in daylight for the first time in 3 years on 27 August. From October onwards almost all bombing sorties were to German targets, Bombing sorties,
Jun-44 Day, 2716 Night, 13270 %day, 16.99
Jul-44 Day, 6727 Night, 8896 %day, 43.06
Aug-44 Day, 10156 Night, 7637 %day, 57.08
Sep-44 Day, 10019 Night, 4524 %day, 68.89
Oct-44 Day, 6758 Night, 8671 %day, 43.80
Nov-44 Day, 5176 Night, 8079 %day, 39.05
Dec-44 Day, 3720 Night, 9864 %day, 27.39
Jan-45 Day, 1303 Night, 8326 %day, 13.53
Feb-45 Day, 3669 Night, 11396 %day, 24.35
Mar-45 Day, 9605 Night, 9247 %day, 50.95
More data is available in the article mentioned by Ewen but from the British official history, for raids on targets in the Rhur during September 1944 by Bomber Command, the day raids were against the synthetic fuel plants, Night 872 sorties, 11 lost, 1.3%, flak damaged 22, 2.5% , Day 1,464 sorties, 19 lost, 1.3%, flak damaged 530, 36.7%. One reason why Bomber Command could prefer night raids.
Other reasons could include
Cloud varies across the day and season, the most clouds are at around 1 PM, around the 8ths usual attack time. Over Europe in summer during the day there are 3 days with no clouds for every 2 nights free of cloud, in winter it is 1 day to 3 nights. This ignores things like fog and mist, which are more prevalent in winter. Then there is the day to day weather, being able to strike day and night gives you options.
The problems of air traffic control if both Bomber Command and the 8th Air Force are operating in daylight, the number of allied escort fighters available, even with the Spitfires with rear fuselage tanks, the German fighter force growth and concentration as the year went on, quality was going down but not numbers within range of the targets. Inexperienced fighter pilots could still do well against weakly escorted bombers with weak defensive armament flying in loose formations. The time of year, Bomber Command started daylight raids against targets in Germany in late summer, then think of the amount of daylight available in the coming winter.
Lancaster VI, a cross between regular Lancaster and Mosquito for pathfinder and master bomber sorties, about 30 mph faster than the regular Lancaster, and 60 mph with the front and mid upper turrets removed, used Merlin 85 engines which had problems, the RAAF using Merlin 60 etc. series as replacement engines for its Lincolns until locally built Merlin 102 became available. Merlin 85 production began in January 1944 and ended in June 1945, 1,420 built. 2 Lancaster VI prototypes serials DV170 and DV199, 7 others modified, JB675, JB713, ND418, ND479, ND558, ND673 and ND784.
DV170 to Rolls Royce 16 June 1943, struck off charge 16 December 1947.
DV199 to Rolls Royce 6 July 1943, RAF Wyton 23 December 1943 to 1 January 1944, back to Rolls Royce, struck off charge 8 June 1947.
JB675 converted November 1943, RAF Wyton 14 March 1944, 7 squadron 14 April, 405 squadron on 1 May, 635 squadron 24 July, 7 Squadron 23 August, flying accident category AC 16 November, 76 squadron 2 December, RAE 17 December, Rolls Royce 20 January 1945, used as an engine test bed, SOC 7 September 1948.
JB713 converted December 1943, RAF Wyton 5 February 1944, 7 squadron then 405 squadron on 21 March, 635 squadron 25 July, lost on operations 18 August 1944.
ND418 converted January 1944 RAF Wyton 16 March 1944, 83 squadron 20 March, 7 squadron 14 April, 635 squadron 24 July, 82 squadron 15 November, RAE 17 December, bomb ballistics unit 28 February 1946, dumped October 1947
ND479 converted January 1944, used by Avro and AAEE, wrecked 26 April 1944.
ND558 converted January 1944, A&AEE 21 May, 635 squadron 26 August, Rolls Royce 11 September, RAF Wyton 16 September, Rolls Royce 28 February 1946, bomb ballistics unit 12 November 1946, still around end December 1949 (reported with Rolls Royce 1944 to 1946.)
ND673 converted March 1944, RAF Wyton 21 June, 7 squadron 25 June, 635 squadron 24 July, completed 23 operations as part of 635 squadron, RAE 11 December 1944, SOC Cat E 31 January 1947.
ND784 converted March 1944 was used as an engine test bed by Armstrong Whitworth and Power Jets, scrapped 1952
The Halifax III had an improved ceiling versus the mark II and V, the Halifax VI (480 production versions built July 1944 to November 1945), is reported to have had a better ceiling than the Lancaster I and III.
Bomber Command fuel loads were calculated according to track miles plus a fixed reserve, after that came what was available for a bomb load plus any weight safety margin for things like take off and altitude performance. Given the weather forecasting and the logistics of landing large numbers of aircraft when the weather turned bad there does not seem to be much fine tuning of fuel loads, just the basic rules.
In gallons the Lancaster fuel load was track miles divided by 0.95 plus a 200 gallon reserve. The Halifax II track miles divided by 0.83 plus a 200 gallon reserve. The Halifax III was track miles divided by 0.8 plus a 200 gallon reserve. The Stirling track miles divided by 0.75 plus a 300 gallon reserve.
So at 800 miles track range the Lancaster fuel load, including reserves, was 1,040 gallons, the Halifax II 1,164, the Halifax III 1,200 and the Stirling 1,367. At 1,400 track miles the figures were 1,675, 1,882, 1,950 and 2,168 gallons respectively. It meant at 800 miles the Lancaster could carry around 4,000 pounds more load than its nearest competitor, the Halifax III, but at 17,200 pounds it was more than the internal bomb bay capacity.
At 1,200 track miles the Lancaster had about 14,150 pounds available for bomb etc. loads, the Halifax III 9,260, the Halifax II 8,320, the Stirling 6,625.
At 1,400 miles the Lancaster is credited with having 12,620 pounds available, versus 7,480 for the Halifax III, 6,600 for the Halifax II and 4,695 pounds for the Stirling.
The early B-17F using standard 8th Air Force tactics would use 1,635 US Gallons to hit a target about 320 miles away, landing with 125 gallons remaining. The major penalty for flying high in large, tight formations from almost start to finish.
