The total duration of an XMM observation should not be less than 5 ks.
The maximum observation length is limited by the maximum possible continuous ground station coverage. Depending on the exact location of the apogee telemetry gap during the XMM mission (see Figs. 79 and 80), the maximum ranges from about 70 to 85 ks. Longer observations must be split up by the proposer and will be scheduled individually. Requests to have long observations extending over more than one continuous visibility period back-to-back (``concatenated observations'') are discouraged, because they require manual intervention; see § 4.9.1.
Note that the XMM scheduling software does not contain the functionality to automatically divide long observations (e.g., 200 ks) into schedulable bits (in the present example, of 70+70+60 ks). Therefore, it is the observer's responsibility to propose only observations that can be scheduled within one target visibility period (which has a maximum of about 70 ks; see § 4.1; Fig. 79).
OM imaging mode science exposures may not be longer than 5 ks each in order to limit the amount of memory allocation by tracking history information.