Hi Iqbal,
System will propose date based on following dates:
1. Material availability date
2. pick/pack date
3. loading date
4. transportation planning date
Pick/pack timing and loading time are derived from the settings of shipping point which determine the material availability date and loading date.
Transit time and Transportation lead time are derived from the setting of route which determine transportation planning date and good issue date.
Hope this answers your questions.
Thanks,
Ajmal