Often it takes me 2 days writing and 2-3 days mixing + mastering. As my learning curve raises i put a lot more effort in the mixing and mastering. I tend to rest my ears every 30-40 mins or go for a walk in the woods to get the song out of my head. I tend to work on multiple projects at the same time.
The templates seems like a good idea. on the flip side using the same instruments CAN restrain the creativity as tracks might sound similar.
Also I work best under pressure - lets say i got 3 h for music I often get much more done than when I got a whole day. I might be lazy… Who knows.
The best of luck