Cross-database page controls are not currently in the product. You might try using a cross-database join to join the 2 data sources into one. See Join Your Data
The Tableau website also has an Ideas section where customers can add, comment, and vote on features they would like to see in the product. Votes are used to help prioritize new features. Our Development team also loves to see everyone's use cases in the comments, which helps them better design features that will meet the most possible needs.
I did not find an Idea for this already, so I recommend creating one: Ideas
Hope this answers your question
You can do this using a parameter. This works well for multiple datasources.
Create a single HOUR parameter for all datasources. Then create a separate calculated field in each datasource linking the HOUR parameter to the views. Add the parameter to your dashboard.
Hope this helps.