Hi Deepika,
Since you are using SNP PDS, the time in the PDS would be rounded to the minimum of one day.
So, in SNP, it would calculate the start and end date using this rough cut PDS.
However, it seems in ECC, when the planned order is getting transferred, it would do the lead time scheduling using individual operation times to the minute level.
This will definitely will create difference in the start date/time, if you are using backward scheduling.
Regards,
Manimaran M.