Flat fields and zenith calibration of polarization angle require the installation to be available to astronomers during the afternoon. Normal LP practice is for handover at 1600 hours, after a series of technical checks. This will have to be moved to about 1400 hours, which is possible but not trivial.
If your programme requires afternoon observing, be sure to make the arrangements well in advance (a month, nominally), as it may involve rescheduling staff. Your support astronomer is the person to ask; failing that, the LPO polarization expert (see appendix J).