Being careful not to repeat the year 1901 mistake, I set the TZ variable before I run R. I have the same set of data that I convert as follows:
dates values
date1 date2
and then plot
plot( date1, values )
plot( date2, values )
To my surprise I end up with the following two...



Zero Inflated Models and Generalized Linear Mixed Models with R.
Zuur, Saveliev, Ieno (2012).