Selecting items from distinct collections with a maximum elapsed acquisition date

[fredliporace]

Harmonization between datasets may require an specific kind of query: to return items from distinct collections such that the maximum elapsed time between the acquisition dates for overlapping regions is less than an specified threshold. This would provide a suitable set to build and validate harmonization algorithms.

Is there any way to provide this with the current extensions? The filter extension limit for a single collection seems to break this use.

I may contribute to specify this further, just need some initial guidance on how that should be done. New extension or incorporated into an existing one?