Questions Regarding MRP

I had a couple of questions regarding MRP. Will be glad if you could answer these:

1. Is it possible to remove the 'in house production time' & 'planned delivery time' from MRP?
   1. If it is possible, what will be the impact of removing the above?
2. Can we change the start/end date of the factory calendar, with or without removing the above?

Please answer the above.

Thank you very much.

Regards