It takes me around 18-24 hours here and there to sequence one entire song. I'll sequence an hour or two at a time. On average, it takes about 2-3 weeks of that spare time to sequence an entire song. It also depends on how long the song is and how complicated the sequences are. I try to sequence what makes sense during a song, so when focusing on one effect, usually the other lights are less distracting.
I sequence in the program xLights on my MacBook Pro and found this tutorial series helped me the most getting familiar with the tools in xLights.