How do you manage your workload when a class requires more time one week than in another? Are there capacity-related costs?

Every week seems different in our busy lives with multiple activities competing for our time. We do a form of capacity planning by determining priorities, estimating how much time is needed, estimating the time (capacity) we have available, and applying our time as best we can to those priorities. Sometimes it feels like we are a factory. When a class requires more attention, how do we adjust our capacity or how do we adjust the workload to best satisfy our priorities? What types of costs do we incur as a result of these capacity-related decisions?

400 words! Thank you!