POSIXct time objects

as.POSIXct(7200,origin="1970-01-01")
[1] "1970-01-01 03:00:00 CET"
t0 <- as.POSIXct(7200,origin="1970-01-01",tz="GMT")
t0 <- as.POSIXct(7200,origin="1970-01-01")
attr(t0,"tzone") <- "GMT"   
as.POSIXct(c("97/11/12 12:45","98/01/23 14:20"),
           format="%y/%m/%d %H:%M",tz="GMT")
[1] "1997-11-12 12:45:00 GMT" "1998-01-23 14:20:00 GMT"