on the dashboard I can see the number of people who completed the survey. How can I track when they do the survey?
There are a couple reporting elements that should help with this.
One is the Response Timeline – it displays a chart showing the number of responses over time:
The other option is the Response Count chart:
This chart show a total count of responses in your survey. If you adjust your report to display only a certain timeframe, both of the above charts will update accordingly.
You can adjust what data displays in your report via filtering:
I hope this helps!