It will take about 2-3 months for Labor Approval. Also, it seems you are confused with 140 and Labor approval. They are not. Once your labor approval, your employer can file 140 for you. You can file I-485 concurrent because you are from Nepal. Once your I-140 gets approved ( 15 days in premium and 4-6 months in regular), you can file for H1b extension based on your I-140 approval for 1 to 3 years.
Better check the trackitt.com website. It has really good info for you. The worst case is your case get audited during labor and your case will be hold for 2-3 years and you can't even file for H1b extension. I wish you a best of luck