What would happen to the length of day if the earth took 40 hours to rotate?

The polar regions would be much warmer all ice would melt and sea levels would rise by hundreds of feet. The equator would be cooler than it is now.

The polar regions, and territories north of the Tropics would experience a more variable climate. The land of the midnight sun (in summer) and of no sun (in winter) would reach much further south, and the Aurora would be visible much further south and might be more spectacular. Climate in general would probably be much different from what we know today.