XMM-Newton is operated in a pre-planned manner. Observers are not expected to be present for the execution of their observations. Thus, all observations must be specified in full detail in advance by the proposers.
The OTAC will consider each proposal based on its scientific merits without any, a priori, preference for programs of any specific size. There are no restrictions on the duration nor the size of the programs except those set by the technical constraints of the mission, such as, for example, sky visibility.
Proposers for ``Open Time'' are not allowed to duplicate any of the planned observations and should carefully justify duplications with performed observations (see section 5.11 for the exact definition and further discussion of duplication issues). Proposers for ``Open Time'' observations should avoid the violation of data rights of planned or performed observations (see section 5.12 for the exact definition and further discussion of this issue). Checks for duplications and violation of data rights will be performed by the SOC during the processing of the proposals.
In total about 90% of XMM-Newton's observing time will be available to ``Open Time'' observations.