In general, policies requested between the 1st and 20th day of the month take effect the following month, while policies applied for between the 21st and the last day of the month take effect the following month plus one.
For example, if you request your policy on September 1st, it will take effect on October 1st, whereas if you request it on October 25th, it will take effect on December 1st.
The exception to this rule applies to newborns, since for them it is possible to request to the insurance company for immediate enrolment.