The amount of time an adult probationer will spend in a probation detention center is set either by a Judge or plea agreement between the criminal defendant and the State. Any PDC sentence must be indeterminate (meaning it has a range of months to serve). For example, a common PDC sentence is 300-365 days; whereas a probationer who has no violations at the detention facility (such as fighting, etc...) will be released after 300 days. Should that probationer accrue violations at the facility - that could delay his release until he has served 365 days.
The shortest PDC sentence I have seen is 90-120 days or approximately 3-6 months. However, it is not uncommon that an inmate will be given credit for the time he has already served in the County Jail prior to sentencing. With credit for time served - any sentence may be considerably shorter.
The Judge signs the order establishing the time to serve on an offense. The Department of Corrections (DOC) presently operates 22 probation detention centers throughout Georgia. Refer to link below for more detail. Depending on the nature of the offense and the judgment & sentence order, probation detention centers are designed to provide short-term confinement of probationers sentenced by the courts, normally for a period of 90 to 180 days. This answer is for informational purposes as I do not practice law in the state of GA. Contact a GA attorney for legal advice. You can find an attorney through Avvo.com and check out the GA Bar Association. See link below.
While of course the judge sets all aspects of a sentence, in my experience I have seen judges relying on state probation officers for input on not only whether detention center treatment was appropriate, but also how long will the subject be waiting (in custody) for a bed space there, etc. At times where there have been such long in-custody waiting periods (usually the probation officer will tell defense counsel, if asked), you can often successfully ask the court to either reduce the time at the detention center or allow the subject to remain free until notified that a bed space has opened up, at which time the subject turns themselves in for transport to the detention center.
The court could set it to a definite number of days or months. Its usually 90 to 120 days but the judge has toe power to set it for a longer period. I have never seen a judge set it for less than 90 days.
One other "warning". If your sentence starts with being detained at the county jail, then any days spent there, waiting for a bed at a facility is NOT credited toward the total sentence at the Probation Detention Center. Hence, the speed at which a slow-moving government agency acts determines how long you are out of commission (jailed). Your attorney should attempt to get you into the county "work alternative" (also called "work release") program UNTIL you are transported to the Probation Detention facility.