More Bismarcks and Less Graff Zeppelins
IOTL the Anglo-German Naval Agreement allowed Germany enough tonnage to build three 35,000 ton battleships.
The Germans used some of this to build Bismarck and Tirpitz. The planned completion dates were 1st October 1939 and 1st February 1940 respectively (39 months to build) but they were actually completed on 28th August 1940 and 1st February 1941 (for an average of 51 months to build).
According to M J Whitley, the third ship Battleship H was to have been laid down on 10th October 1937 for completion on 1st January 1941 (39 months to build). In January 1937 the Germans calculated that the British plan to build Duke of York, Anson and Howe allowed to them to build a fourth 35,000 ton battleship and they planned to lay down Battleship J on 1st May 1938 for completion in 3½ years (which would have been 1st November 1941).
However, Battleships H and J weren't laid down until 15th July 1939 and 15th August 1939 respectively and were cancelled after World War II broke out.
Meanwhile Aircraft Carriers A and B were ordered in 1935 for completion on 1st April 1939 and 15th November 1939. According to Whitley Aircraft Carrier B was laid down on 30th September 1936, but hadn't been launched when World War II broke out and was scrapped on the slip. Her sister ship wasn't laid down until 28th December 1936, but was launched as Graff Zeppelin on 28th December 1938. However, work on her was suspended in June 1940 and she was never completed.
ITTL the Germans decide to convert a merchant ship to an experimental aircraft carrier to gain operating and design experience for a class of bespoke aircraft carriers to be built in the first half of the 1940s. This releases resources to build other warships in the second half of the 1930s.
Therefore is it possible to lay down a third Bismarck in September 1936 in place of Aircraft Carrier B and complete her in 51 months, that is December 1940? The dimensions are about the same size, Graff Zeppelin is longer and Bismarck is beamier. However, Bismarck is about 10,000 tons heavier, could the slipway take the extra weight?
Graff Zeppelin had more powerful machinery than Bismarck. Therefore I think the major stumbling blocks would be: the main and secondary armaments; the fire control equipment; and finally the armour.
More Light and No Heavy Cruisers
What if the Germans also built a sextet of 8,000 ton light cruisers with combined steam and diesel machinery (COSAD?) instead of the 5 Hipper class? The sixth ship would use the slipway used by Graff Zeppelin IOTL.
These light cruisers would be an enlargement of the Nurnberg design or the Kreuzer M. They would be better suited to the commerce raiding role. As they consumed less of Germany's scarce industrial resources than the Hipper class it might be possible to complete all 6 of them in the time it took to complete the first 3 Hippers IOTL.
A third Bismarck and 3 extra cruisers would not change the course of history, but they would be a better investment for Germany than the 2 incomplete aircraft carriers and 2 incomplete heavy cruisers of OTL.