oh how time flies...IBM's mark davis has a proposal about "handling different binary formats of datetime". this is something i'd never given any thought to but one glance at table 1 (reproduced below) in the proposal makes me wonder why this hasn't come up before.
|JAVA_TIME||int64||milliseconds||Jan 1, 1970|
|UNIX_TIME||int32||seconds||Jan 1, 1970|
|ICU4C||double64||milliseconds||Jan 1, 1970|
|WINDOWS_FILE_TIME||int64||ticks (100 nanoseconds)||Jan 1, 1601|
|WINDOWS_DATE_TIME||int64||ticks (100 nanoseconds)||Jan 1, 0001|
|MAC_OLD_TIME||int32||seconds||Jan 1, 1904|
|MAC_TIME||?||seconds||Jan 1, 2001|
|EXCEL_TIME||?||days||Dec 31, 1899|
|DB2_TIME||?||days||Dec 31, 1899|
java and Unix while having the same epoch (origin) differ in datatype and units so they differ in accuracy and range. windows' time scales differ internally for OS vs file system (no snickering). at the current state of this proposal, he's chosen to use Windows datetime as a "universal 'pivot'". that gives a time scale range from 29,000 BC to 29,000 AD. i guess IBM really does take the long term view ;-)
if you want to provide feedback i guess you'll have to join the ICU mailing list.
so now you know.