Hi,
1. The best to export all the orders of one day only one time is to use the trigger "Every days". But that will export all the orders, not only the orders of the desired day so there will be double entries. A solution could be to create a specific order field, then in the mass action set an action to fill that custom field with a value, and then still in this same massaction add a filter on that custom field. That way, the mass action will be launched every days, and get all the orders without the specific value in the custom field. Hope this is clear enough
2. The limitation part allow to, in this case, restrict the number or orders which will be exported. This is useful to not have too many data which could create a timeout, or will consume to many resources.