use strict;
use warnings;

my $expiry = time + 3600;

my $time;
my $previoustime;

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