Preserving the class of POSIXt objects

Dear all,

I am working with a list of objects each of which contains two POSIXct
objects (say, $Start and $End) and a number of different data in
addition to that. Now an easy way to extract Start times of all object
could be sapply(x, "[", "Start") but this converts them all to
numeric, and so does sapply(x, "[[", "Start"). lapply preserves the
class but is obviously a list rather than an atomic vector but using
unlist is a way of getting rid of the class again. I know the vector
can be converted back using as.POSIXct and that one can set the class
attribute back to "POSIXct" but is there an easier trick that I can't
just figure out? Thanks in advance for any suggestions.
...