[R] Where to learn how to deal with time class variable?

[Kerry Bush]

Dear R-helpers,
  In my data set, I have a time variable 'RecordTime'
whose class property is 'times'. When I list my data
set, I see the values of RecordTime is like 10:20:30
in a 'h:m:s' format. Suppose I want to choose all the
data after 10 o'clock, then use

subset(data,RecordTime>10:20:30)

just doesn't work. I noticed that all the values of
RecordTime seem to take some decimals when using
str(data). But how can I easily find the
correspondence between those decimals and the exact
times? I have looked at the help file of POSIXlt and
related functions. Yet I couldn't find any useful
instruction on this issue.