Measuring Training Effects on Task Efficiency in Your App

Hi, How can I measure a training effect? I have a task flow people can do in my app - ordering a service And I'm to learn whether people become more efficient (measure by time to complete the task) the more they are doing the task The hypothese - In the first time they are completing the task, it will take them longer time than in the second and third and so on... Is there a way I can achieve this kind of analysis? Thanks!