Let's do this top-down.

if (valid_state($pull_downs) && $start_time < $end_time) {
    # okay; put processing here
} else {
    # not okay: yell at user.
}
[download]

For this to work, we need to satisfy some conditions. First, we need to bump all the pull-downs together; and second, we need the start and end times to be in some comparible format. Fortunately, these are both easy tasks. Then we have to write the valid_state functions, which isn't hard either.

# put this before the if mentioned above
my $pull_downs = join "", $pull_down1, $pull_down2, $pull_down3, $pull
+_down4;

# or, if you're using CGI.pm, something like this:
my $pull_down = join "", map { $query->param("pull_down$_") } 1 .. 4;

# (whatever works; just mash them together. $pull_downs now looks like
+ your binary numbers.


# And this returns true only if the number is one of your valid ones:

{
  my $valid = qr/^(0000|1000|1010|1100|1111)$/;
  sub valid_state {
    return shift =~ $valid;
  |
}
[download]

You may need to do a little extra work to binarify the data from the pull-down to your internal format, but that shouldn't be too daunting by now. As for the times, a good way of making them compatible is to translating them (say, with DateTime) to epoch seconds. These are simply two numbers, the bigger one represents a later time.