In my experience when I had 1 Mbps upload speed on my old DSL internet connection it would take me 2 1/2 hours to upload a 1 GB file from my internet connection.
So you can expect the 1 GB file to take at least 2 hours to upload depending on network congestion.
When uploading a 1 GB file or larger on 1 Mbps upload speed I would start uploading it and then leave the computer and do something else.