Different regions have different regulations. Usually 30 minutes, with automatic timing equipment. If it does not involve underworld or state secret crimes, there is generally no public security personnel present to supervise and no one will disturb it.
During criminal detention, lawyers may apply to meet with criminal suspects. If the case does not involve state secrets, the public security organ will arrange a lawyer to meet the suspect within 48 hours. Under normal circumstances, investigators will be present to accompany them.