[R] Converting time from HH:MM:SS to only HH:MM

[Neotropical bat risk assessments]

Hi all,

I need to compare between times and put all similar times in specific 
1 minute bins.
Unfortunately the original data include seconds as well.

My data is in HH:MM:SS format but I need it rounded to only HH:MM and 
trying in Excel to display "unique" records only does not work since 
the seconds are not unique.

Is there an easy way using perhaps CHRON to change all from the 
HH:MM:SS data to a new HH:MM only data set and save as a TXT or CSV file?

Tnx