RTS you say. I have a engine for RTS game plus multi player only good for windows. Its not quite complete, it would be good for demos plus a bit more.
It has a build menu working, has spell buttons,drop ships can attach to objects or carry them inside, Units , vehicles planes, towers, buildings , plants, are the base types with them you can create as many different types you have assets for. Has a very crude map editor menu creator and asset library editor.
the Library is where you define all your objects for any one game type.
May not work on newer OS only windows a port would not be doable. this is what its at now.
you could try down loading the demo you need the folder ShipRTS and the folder UpDatedFullscreenRTS it ships with the run time for VC10 and DX10. the server is down so it will not connect but if it loads and starts the menu system the engine would work on your windows OS.
The links seem not to work on my iphone not sure.
As for time well you would need to work out what format to hold you graphic objects in, how you load and create them, you probably need to write or have written some form of
helper apps like asset creator, map editor, Unit testing apps, work on sound the demo needs sound.
it's going to take a lot of time, but the more modular the program is the less of a pain implementing new object into the system will be.
I may not be able to help I feel burnt out or no longer get a kick out of programming this RTS engine(may post the lot on hosting site). I've taken 4 month of so far no programming.