To cite in publications use:

David James and Kurt Hornik (2009). chron: Chronological Objects which Can Handle Dates and Times. R package version 2.3-33.

Corresponding BibTeX entry:

  @Manual{,
    title = {chron: Chronological Objects which Can Handle Dates and
      Times},
    author = {David James and Kurt Hornik},
    year = {2009},
    note = {R package version 2.3-33. S original by David James, R port
      by Kurt Hornik.},
    url = {http://CRAN.R-project.org/package=chron},
  }