Can you provide a bit more detail?

In the R Help Desk 2004 (http://www.r-project.org/doc/Rnews/Rnews_2004-1.pdf), Gabor Grothendieck recommends chron over POSIXct classes on account of the time zone conversions which occur when the tz attribute of the latter object is not "GMT". Will this not be a problem with lubridate? Thanks in advance.

I've never found that to be a problem in practice. Do you have an example where it's bitten you in practice?

(Also you should use UTC and not GMT)

Hi Hadley, yes for instance

> as.chron("1970-01-01")+unclass(as.chron("2001-04-01")) [1] 04/01/01

> as.POSIXct("1970-01-01","EST")+unclass(as.POSIXct("2014-06-01","EST")) [1] "2014-06-01 05:00:00 EST"

If there is any conversion necessary it is difficult to get back the original intended time.

What does adding two dates together mean?

Isn't this the conventional way of converting variables which have been coerced to their numeric representations back to time/date classes?