Description: set ticket to be due in a specified number of business hours (so that weekends and nights are excluded)

Uses Jesse Vincent's Business::Hours library, available from CPAN

Condition: On Ticket Creation
Template: Global template: Blank
Action: User Defined

Custom Action Preparation Code: return 1;
Custom Action Cleanup Code:

my $duedate = RT::Date->new($RT::SystemUser);
my $hoursuntildue = 4;
use Business::Hours;
my $hours = Business::Hours->new();
my $curtime = time;
my $bus_hours_duetime = $hours->add_seconds ($curtime, ($hoursuntildue*60*60));
$duedate->Set(Format=>'unix', Value=>$bus_hours_duetime);
$self->TicketObj->SetDue($duedate->ISO);
return(1);

This takes care of the case in which TimeLeft is modified after ticket creation:

Description: Upon editing, convert TimeLeft into business days

Condition: User Defined
Action: User Defined
Template: Global template: Blank
Stage: TransactionCreate

Custom Condition:
 if ($self->TransactionObj->Field eq 'TimeLeft') {
  return(1);
 } else {
  return(undef);
 }

Custom Action Preparation Code: return 1;

Custom action cleanup code:
 my $duedate = RT::Date->new($RT::SystemUser);
 my $hoursperday = 9;
 my $hoursuntildue = $self->TransactionObj->NewValue()*$hoursperday;
 use Business::Hours;
 my $hours = Business::Hours->new();
 my $curtime = time;
 my $bus_hours_duetime = $hours->add_seconds ($curtime, ($hoursuntildue*60*60));
 $duedate->Set(Format=>'unix', Value=>$bus_hours_duetime);
 $self->TicketObj->SetDue($duedate->ISO);
 return(1);