I got it issued on handing over the Pay Order within 30 mins.
Told the sales guy before hand a day earlier when I visited the showroom that I will only book through them if they are willing to issue a PBO on the spot.
They can issue it immediately (provided the internet is working and it's not Saturday as dealerships are open on Saturday but Toyota Indus isn't.
So if you booked on Saturday .. you should get it on Monday morning. On any other day (Mon to Friday - You should get it on the spot - and its not a number only its a bar coded form which includes all the details of booking)