What is the ideal time interval for a jockey pump to automatically switch on and off? Is it normal to have a hammering sound after the pump switches off?

Jockey pumps usually switch on and off on a pressure sensor. You should not have pump starting more than 4-5 times per hour because of the motor protection. You can reduce number of starts per hour by properly sizing pressurisation vessel.

Hammering sound that you hear is the check valve closing. That is normal.