DURation specifies the length of the current scan. Usually this is used instead of STOP. It is assumed to be a UT time interval unless LST was specified, in which case it was assumed to be an LST time interval. DWELL is a very similar parameter except that, with DURation, the scan starts GAP seconds after the previous stop time while with dwell, the scan will start at least GAP seconds after the previous stop time, but, if necessary, will wait longer to allow all antennas to reach the source.
Note that DUR and DWELL may be both be used in the same schedule, but cannot both be used for the same scan (that would not make sense). If either is used, the time specified overrides any previous specification of the scan length made with either parameter.
Once the scan start time has been specified as above, it can be adjusted further with PRESCAN. Then the actual time that recording starts is adjusted further with MINPAUSE and PRESTART. PRESTART, MINPAUSE, and PRESTART allow the user to start recording early to give the correlator a chance to synchronize before the start of good data. This should no longer be needed for correlators currently in use. These parameters also can help prevent short stoppages which can cause problems with playback. Again, this is not really a problem with the disk systems like Mark5. See the descriptions of those parameters for more information. The SCHED defaults are generally reasonable so, if you are not an experienced user who wants to exercise fine control of recording management, don't worry about these parameters.
The start and stop times reported in the summary and operator schedule files are the same for all stations. They take into account any adjustments made as a result of specifying PRESCAN, but do not take into account adjustments requested using MINPAUSE and PRESTART, since those can be station dependent.
See the Scan Times section for more information on the specification of scans.