This is another of the items that I felt was very unrealistic, time wise. I was disappointed not to be able to find a mod that worked for these either. It's taken me a few weeks to get it figured out. I found an outdated one on MTS but it didn't work.
The trick seemed to be I had to add the resume options to the file also. I didn't know we could even resume the music until I studied this. But I did find the resume is not an actual resume, it takes almost as long to do a resume as it does to write a song. I would get so frustrated when a sims had to go to work or school and I'd loose all that work.
There are sheet music sheets created in your sims inventory that can now also be done quickly. They do have to be songs that have been written...not Lyrics or Jingles. I've been working on those options too, but have not been able to get them much faster.
This mod works for guitar, violin, piano, keyboard, and the organ.