The detention notice states that the person will be detained for 7 days, but why is he not released after 7 days? Can I continue to add time after 7 days?

If the detention notice you receive states 7 days and you are not released after 7 days, it means that the case has been transferred to criminal investigation. It needs to be handled in accordance with the procedures for handling criminal cases.

The 37 days stipulated by the law does not mean that you can come out within 37 days. If the procuratorate approves the arrest within 37 days, the person cannot come out. If the arrest is not approved and the investigation needs to continue, the person can be converted to bail. A person can be released while awaiting trial or under residential surveillance.