R Studio Randomize Date and Time

I want to anonymise a dataset by replacing the original dates and times columns with new, randomized dates (from 01.01.2012 till 31.12.2015) and new, randomized times.

• Format of the date column: d%.m%.Y%

• Format of the time colum: h:m

The dataframe consists of 37.094 rows.

Any ideas?