the amount of time i spend on a song varies widely. It took me almost oh, 20 hours of work to finish my Battle Resonance song, and almost 15 hours to make my A Past Forgotten song. I just made a crystal resonance song in about 3 and a half hours, but after listening to it i feel i still need to tweak it. I have another song called Serenity i'm currently stuck on, i've spent about 8 hours on it so far (much less considering i needed very little tweaking on part of the voices and it doesn't have very many notes). It took me 2 hours to get that stupid piano voice sounding good though.
To be honest i just don't spend that much time on a song. Usually, a song will sound way, way better if i complete the vast majority of its melody in under 4 hours. This one i was able to polish in just 1 hour.