Difference between In house production time and Production order basic dates

Hi Experts,

For two materials client has maintained in house production time is 1.

But in production order for one material system taken production time as one day.

for another one material system taken production time as more than one day.

can any one please explain me what could be the reason for this?

and dependent parameters for basic dates and scheduling dates calculation.

Thanks in advance.

Regards,

BLESSING