trying to compare POSIXct objects in if statements within functions- R studio : I have something like this within a function:
x <- as.POSIXct((substr((dataframe[z, ])$variable, 1,
    8)), tz = "GMT", format = "%H:%M:%S")
print(x)
if ( (x >= as.POSIXct("06:00:00", tz = "GMT", format = "%H:%M:%S")) &   (x <  as.POSIXct("12:00:00", tz = "GMT", format = "%H:%M:%S")) ){
   position <- "first"
}


but I get this output:
character(0)
Error in if ((as.numeric(departure) - as.numeric(arrival)) < 0) { : 
  argument is of length zero

how can I fix this so my comparison works and it prints the correct thing?