1-add date/time field  and name is  x_studio_old_order_date 

2-and read only add condition state == "sale"

3-add automation

1. Model=sales order 
2. trigger statin=sales order 
3. apply on [('state', '=', 'sale')]

4- add python code 

if record.x_studio_old_order_date:

    record.write({

        'date_order':record.x_studio_old_order_date

    })

for inventory same step 

add date/time field on inventory receipt

invisible state == "draft"

required x_studio_old_order_date

readonly state=="done"

add an automation rule

and add python code 

if record.scheduled_date:

    record.write({

        'date_done':record.scheduled_date

    })