Use the Pareto Principle
Ever heard of the principle 20% of what you do, gives you 80% of the value. The principle derives from an Italian Economist who found that 80% of the land in Italy was owned by 20% of the population. Since then it has been extended to many situations and more recently into a typical working day in an office where it was found that in a typical 8 hour day people were really only doing productive work in 90 minutes.
In practice what you should be doing is to figure out what the most important things that you do to give you the most value. To relate it to pet sitting, you may find that dog walking is your most profitable service compared to cat sitting. By maximising your work to doing more dog walking than cat sitting will increase your profit and get you on track to growing your business.