I've just been messing with sending IPC_GETOUTPUTTIME and I don't seem to get sensible results when using it with mode 1 (i.e. return time in seconds).
It seems to work fine in mode 0 (i.e. return time in milliseconds) but mode 1 just returns rubbish.
I'll just have to work with mode 0 for now, that's fine.
(I'm using Winamp version 2.77)