my $day1_prog1_start = Date_to_Time(2007, 8,  8, 17, 0, 0);
my $day1_prog2_start = Date_to_Time(2007, 8,  8, 23, 0, 0);

my $day2_prog1_start = Date_to_Time(2007, 8,  9, 17, 0, 0);
my $day2_prog2_start = Date_to_Time(2007, 8, 10,  3, 0, 0);

my $day3_prog1_start = Date_to_Time(2007, 8, 10, 17, 0, 0);
my $day3_prog2_start = Date_to_Time(2007, 8, 11,  1, 0, 0);

my $day1_prog1_len = $day1_prog2_start - $day1_prog1_start;
my $day2_prog1_len = $day2_prog2_start - $day2_prog1_start;
my $day3_prog1_len = $day3_prog2_start - $day3_prog1_start;

my $avg_prog1_len = $day1_prog1_len / 3
                  + $day2_prog1_len / 3
                  + $day3_prog1_len / 3;

print("Prog2 usually starts $avg_prog1_len seconds after Prog1 start.\n");

my ($year, $mon, $day) = Today(1);
my ($hour, $min, $sec) = (Gmtime($day1_prog1_start))[3,4,5];

my $next_prog1_start = Date_to_Time($year,$mon,$day,$hour,$min,$sec);
my $next_prog2_start = $next_prog1_start + $avg_prog1_len;

my $next_prog1_start_str =
   strftime('%Y/%m/%d %H:%M:%S', gmtime($next_prog1_start));
my $next_prog2_start_str =
   strftime('%Y/%m/%d %H:%M:%S', gmtime($next_prog2_start));

print("If Prog1 starts at $next_prog1_start_str,\n");
print("Prog2 will likely start at $next_prog2_start_str.\n");

##</code><code>##

Prog2 usually starts 10800 seconds after Prog1 start.
If Prog1 starts at 2007/08/09 22:00:00,
Prog2 will likely start at 2007/08/10 01:00:00.