As it has already been mentioned, the Herschel observing time is divided into Guaranteed Time (GT) and Open Time (OT). Of the total available observing time 32% is GT, i.e. 6328 hours for the 3 year mission. The remaining 68% of the time is awarded as OT, i.e. 13448 hours for the 3 year mission. A maximum of 4% of the Open Time can be allocated in programmes as Director's Discretionary Time (DDT).
The GT holders and their allocated times are as follows:
Instrument Principal Investigators (PIs) each own 30% of the GT, thus each instrument PI owns 1898 hours of GT.
The Herschel Science Centre (HSC) owns 7% of the GT, thus the HSC owns 443 hours of GT.
Mission Scientists (MSs) each own 0.6% of the GT, thus each MS owns 38 hours of GT.
The Herschel Optical System Scientist (HOSS) owns the same amount of time as an MS, i.e. the HOSS owns 38 hours of GT.