"There is no average time to complete an API integration of a software application. The time it takes depends on many factors, both within and outside of the control of the application integration engineer. Some of these include the IT environment, the other programs the application is interacting with, the nature of the API, and whether the applications are hosted on-premise or in the cloud. An example of this variation in integration times is that integrating an HTML version of an (API) may typically take less than an hour to complete. In contrast, integration of the XML version of the same API could take up to 20 hours, due to its complexity."
