I have two suggestions; one regarding research, and the other about buildings.
1. Create a new research tree for resources. When you complete the research, you would get x % more resources. It could be generic, meaning you just research "resources", or it could be specific, like you research "oil"; every level of research you complete would get you x % more oil.
2. The first level of any given building should only take 30 minutes (at most) to complete. This would speed up the game in the early stages. Or, at a very minimum, the length of time to build a new airfield should be drastically reduced. There's no good reason a new naval base should be complete in 15 minutes, but an airfield should take 18 hours. I mean, level out the ground and throw some steel mesh down and you're good to go.
1. Create a new research tree for resources. When you complete the research, you would get x % more resources. It could be generic, meaning you just research "resources", or it could be specific, like you research "oil"; every level of research you complete would get you x % more oil.
2. The first level of any given building should only take 30 minutes (at most) to complete. This would speed up the game in the early stages. Or, at a very minimum, the length of time to build a new airfield should be drastically reduced. There's no good reason a new naval base should be complete in 15 minutes, but an airfield should take 18 hours. I mean, level out the ground and throw some steel mesh down and you're good to go.