It all depends upon the circumstances. Usually it takes as long as it reasonably takes police to complete their investigation. That can be more than 72 hours which is usually the limit for holding you before they must bring you before a Judge for arraignment. If you contact a lawyer and decide to challenge their detention of you, your lawyer must argue that the police are keeping you longer than is necessary under the circumstances of this case. If a judge agrees with you and your lawyer then any criminal charges that resulted from your detention may be dropped or never brought at all. So be vigilant and don't accept the police abusing you by not arresting you while they continue to hold you indefinitely. Call your lawyer and challenge it. Remember, police detentions are voluntary unless you or your attorney ask for you to be able to leave. If the police should detain you without formally arresting you, then it's a good idea to ask if you are free to leave. If the officer says you may leave, then its time to get out of there quickly. Otherwise, you could be considered as staying voluntarily and that could make the stay legal.