Hi Peter,
Just to clarify, are you wanting to have MTS+MTO, as well as to automatically trigger the reorder rules immediately on confirm? So as soon as you confirm a sale order it makes purchase orders for both stock that's required for the order (MTO), as well as for your stock replenishment (reorder rules)?
If so, as far as I can tell there's no way to do it without creating a custom module. If you're capable of developing an app, I've added some notes below.
You could either hook the action_confirm method of the sale order or create an automated action in order to get some code to run when you click confirm. This would allow you to run the scheduler as soon as the order it confirmed.
However, you mentioned that this function is taking hours (how many products/rules do you have?), so you would need a way to limit this to only the products that were in the related sale order. The easiest way I can see is to call the_procure_orderpoint_confirm function with a context containing the products, and to hook the _get_orderpoint_domain function on the procurement.order model to add that into the domain to select only the relevant reorder rules.
Cheers