There is no "timeframe". However it's always best to contact the authorities ASAP.
I will be happy to speak with you at no cost with a FREE phone consultation if you have a San Diego or California matter. Please call my office at 619-238-1905 or visit my website at www.lawofficeofwilliamdaley.com
There is a statute of limitation to bring a prosecution. It is suggested that your friend contact the police as quickly as possible in order to preserve evidence and to ensure that memories are fresh.
The victim can take as long as the victim wishes to make a report in reference to a criminal matter. There is set time limit. However, the longer the wait , the less likely the DA is to prosecute.
The above is not intended as legal advice. The response does not constitute the creation of an attorney client relationship as this forum does not provide for a confidential communication.