Once you add a keyword, SearchVitals fetches an initial ranking quickly — usually within a couple of hours. After that, each keyword is re-checked roughly once a week.
If you need a more current number before the next scheduled check, use the manual refresh button next to that keyword (available on Basic plan and above).
If you downgrade to the Free plan while you still have tracked keywords, you'll continue to see your last tracked rankings as a frozen snapshot — they just won't refresh anymore until you upgrade again.