One OB, which includes overheads, should not exceed 30 minutes (1800 sec) of on-source time. In case of Subaru observations one queue OB is translated into one command that is sent to the telescope control system. There is no lower limit for OB total time, and we strongly encourage to make them short, in order to minimize the probability of interrupting one by an emergency situation (sudden weather breakdown, telescope malfunction, etc.). If such situation occurs, the affected OB or exposures will be repeated. However, the general policy is to finish an OB once it has been started.
Due to the specific filter changing procedure, exposures in two filters should be defined as two separate OBs. Two consecutive observations of different exposure times are also not allowed as one OB.