Im facing issue with periodic alert..
The above doc is talkng abt event based alert..
First verify its firing at scheduled time only.
What is the format of message, detail or Summary?
If its summary make sure its grouping it correctly. Anything above ********** it will send separate mail.
Provide the scripts and screen shots of your alert.
As I know if you gave detail type, it will fire multiple times.
So give type as summary and in email text don't remove standard template.