use strict;
use warnings;

my $expiry = time + 3600;

my $time;
my $previoustime;

sub mysleep {
      printf 'before sleeping: time = %d, $time = %d, %s', time, $time, "\n";
      sleep shift;
      printf 'after sleeping:  time = %d, $time = %d, %s', time, $time, "\n";
}

while ( $time = time
        and $time + 300 < $expiry
        and ( $time - $previoustime >= 10
              or mysleep (10 + $previoustime - $time)
            )
      ) {
  $previoustime = $time;
  warn $time;
}