I inserted the code but I cannot see any statistics, is there any delay?

There is no delay, you should be able to view online visitors in real-time.

Activation takes place within a few minutes once the account has been created, the Javascript code has been uploaded, and your first visitor (including you) has reached the site.

Some reports can take up to 30 minutes to populate, but Online VIsitors works immediately.

Some statistics won't be available until the respective time period has lapsed, e.g. forecast, weekly statistics, etc.