With prior approval by OTAC (see § 3.5.3), it is
possible to perform a series of exposures where a filter sequence is
repeated, e.g. 'U , UVW1 , UVM2' - 'U , UVW1 , UVM2'-
'U , UVW1 , UVM2',...
The recommended configuration is Science User Defined mode with one window in Image mode and possibly an additional Fast mode window. The minimum exposure time will be 800 s except if Fast mode, which requires a minimum exposure time of 1200 s, is used (see section 18.104.22.168).