The Server knows that there are 20 units on the pallet, but it cannot access the individual processing times for each product without using process logic. Use a Search step to find all the units on the pallet and add the individual processing times to a state on the pallet, then use this state variable as the processing time on the server.
To do this, use a process on the Before Processing trigger. Add a Search step to search the QueueState 'ModelEntity.BatchMembers' (and set the Limit property to 'Infinity'). Create 1 state variable on the model - TempStateName, and 1 on the ModelEntity - TotalProcessingTime. Then on the Found branch put as Assign step to assign a State variable the value of the individual processing time for each unit. Setup the Assign state like the following: State Variable: TempStateName, New Value: TempStateName+ (Unit processing time). TempStateName is a variable used to collect the sum of the unit processing time and save that value to the state on the pallet. Then on the Original branch put another Assign step:State Variable:ModelEntity.TotalProcessingTime, New Value: TempStateName. Then add an Assign to reset the TempStateName to 0. On the Server's Processing Time property, put 'ModelEntity.TotalProcessingTime'