Just as you can download a work area at any time, you can also upload your completed work at any time.
Downloading work areas or packages, and uploading your work require an active internet connection, so you may have issues if you are working in a rural area with no mobile network signal. However, you can upload at any time when you are online.
When moving from one area to another, or from one work package to another, you MUST upload before you will be allowed to download your next work list.