45 minutes - 2 hours
Three main problems for me :
1. The plastic pryer (green) didn't work well for me. It was finally crumpled. So I used a small flat-head screw-driver instead. Slightly scratched the nano but not significant.
2. I have no lead-removing strip. But a rather big vacuum one. Successfully cleaned up one hole. The other two holes, I melted the lead and quickly inserted the wire in. Not too difficult with proper clamping. What's quite nervous was I was afraid that I would've heated the hole for too long.
3. Sliding the inner parts back into the shell left some glue residue on the inside of display cover. I had to slide things back off, cleaned the inside of the display cover with alcohol, placed a long sheet of thin paper to shield the inside of the display cover, slid the whole things in, and pulled the thin paper out. Quite messed up in practice, but it's OK overall.
Work perfectly. Can't be happier. The battery is charged faster and holds the energy longer. Seems even better than when I first had the nano.
The delivery was much faster than the expected.
I'm an experienced electronic/digital DIYer. I still faced some situations that I had to decide and develop my own way to get things proceed. A little more detailed steps and some explanation of parts may help people develop their alternative solution, if they need to.