To cite lubridate in publications use:

  Garrett Grolemund, Hadley Wickham (2011). Dates and Times Made Easy
  with lubridate. Journal of Statistical Software, 40(3), 1-25. URL
  https://www.jstatsoft.org/v40/i03/.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Dates and Times Made Easy with {lubridate}},
    author = {Garrett Grolemund and Hadley Wickham},
    journal = {Journal of Statistical Software},
    year = {2011},
    volume = {40},
    number = {3},
    pages = {1--25},
    url = {https://www.jstatsoft.org/v40/i03/},
  }