You've just canceled your subscription, you expect to revert back to Free plan. Is it immediate?

The downgrade doesn't happen immediately after the cancellation. Depending on your previous plan's expiry date, the downgrade only happens once the previous plan's cycle ends.

1. For example, you are in a Standard Plan. 
2. You've paid the current bill, and the next bill will only arrive in 5 days afterward. 
3. You decided to cancel the Standard Plan to revert to Free Plan now.
4. So you will have five more days of the Small Business Plan's cycle.
5. All the premium features remain with you.
6. Until then, the downgrade will not happen yet.
7. After 5 days, you check your Billing plan again, you will notice that it is now Free Plan.