Workcenter formula for Heat treatment

Dear All,

Please find below my scenario :

I have a heat treatment furnace. Different sort of components are loaded inside the furnace through jig.

For eg., Production Order quantity is 25.  Lot size is 10. Heat treatment time is 60min / run.  (the lot size will vary , depends on the size of the component. In this case, we can load only 10nos of this material).

In this case, we need to run 3 times the heat treatment furnace. Hence it takes 180 min. But the current workcenter formula will give 150min.

Please let me know, how to arrive at the workcenter formula for this scenario.

Thanks

Srinivasan