ows = Open Geospatial Consortium Web Service
Read more about XML Prefixes
So, this ows is NOT part of SharePoint internal field name.
Short post, just feel a bit irritated when someone try to mislead me. On top of that, found a good reference list for SharePoint internal field names.
Calculated Field column can be use effectively to get the differences or duration between two date time. There is a list of useful formula in MSDN: Calculated Field Formulas. But some of the formula is actually quite buggy and not providing the accurate result. Another difficult part is to get the result in the preferred format.
Just to share some of the formula I modified recently to get accurate calculation and in my desired format.
Format: d hh mm (Day Hour Minutes)
=DATEDIF([Start Time],[End Time]-(MOD([Start Time],1)>MOD([End Time],1)),”d”)&” Day(s) “&TEXT(MOD([End Time]-[Start Time],1),”hh”” Hour(s) “”mm”” Min(s)”””)
Format: hh mm (Hour and Minutes)
=(DATEDIF([Start Time],[End Time],”d”)*24+HOUR([End Time]-[Start Time]))&” Hours(s) “&MINUTE([End Time]-[Start Time])&” Min(s)”