x <-80

 test <- seq(from=as.POSIXct('x - 1',format='%M'),to=as.POSIXct('x +
 1',format='%M'),by='sec')
 # this doesn't actually work

test <- seq(from=strptime(x - 1, format='%M'),
            to=strptime(x + 1, format='%M'),
            by='sec')

tmp <- seq(strptime(paste((x-1)%/%60, (x-1)%%60, sep=":"), format="%H:%M"),
           strptime(paste((x+1)%/%60, (x+1)%%60, sep=":"), format="%H:%M"),
           by='sec')
as.numeric(format(tmp, "%M.%S"))