There are two different scenarios when flashing a Meadow board:
1. First use or after formatting
2. Application update
In case 1, flashing should take about 1 minute as some supporting files have to be written to the device as well as the application. These supporting files contain the runtime libraries.
In case 2, the VS extension will not upload any files that has not changed and so flashing should be quicker, in the order of seconds.
We have had some reported cases where deployment has taken 20 minutes. The first thing I would do is to reflash the OS and reformat the file system with the latest software. We have seen that work for some people.
We have a troubleshooting guide which may help to determine if you have a problem we have not seen before.
There is also a public Slack channel - go to the bottom of the page and clock on the Slack icon to subscribe.