Greetings Adi,
I would recommend using Task Lists do define the Operations you need with the UoMs that you require. Then when creating a new Order include the generic Task List.
Also, please consider any effect that setting up the Work as a time unit different from HR will have on your scheduling - you might want to use the Calculation Key of 0 (manual) for your Operations, or you might want to use a negative Exponent in the UoM definition if you do not want the Operations with drains to have a duration to speak of to affect your scheduling.