I don't want to collect data from my plug-in data sources (e.g., MicroStrategy or Tableau) until my sources have completed loading. How can I tell Metric Insights that my sources have been loaded and that collection can begin?

There are a few ways to accomplish this.

1.) One way is to define a data refresh trigger that is externally triggered (see image below).

To learn more please visit this article: http://help.metricinsights.com/m/Automating_the_Collection_of_Data/l/104472-establish-an-externally-triggered-data-collection-trigger

2.) Another way is to define a data collection dependency. Your data collection trigger can be defined to check on a regular schedule (once per day, etc.) but is attached to a data dependency. The data dependency runs against your data source and can check for count of total records, calendar_date, etc. and returns a true/false if satisfied. This is a defined query which provides some assurance that the data jobs are completed and sources are loaded. The dependency can run regularly (e.g. every minute) within a certain time period after you anticipate your data jobs to have completed (e.g. every minute after 7am through 12pm).

You can find more details how to setup a data dependency in this article http://help.metricinsights.com/m/Automating_the_Collection_of_Data/l/104474-set-up-data-dependencies-for-a-data-collection-trigger