We agreed in ODATA-70 that Edm.Time should be xs:duration. ODATA-70 resolved the issue in [CSDL]; this issue is to track resolution in [ATOM].

Here is the definition of time from [URL]:

time = "time" SQUOTE [ sign ] "P" [ 1*DIGIT "Y" ] [ 1*DIGIT "M" ] [ 1*DIGIT "D" ] [ "T" [ 1*DIGIT "H" ] [ 1*DIGIT "M" ] [ 1*DIGIT [ "." 1*DIGIT ] "S" ] ] SQUOTE