Filter by 'time spent viewing email'

[KStockdale]

I'd like to be able to filter by 'time spent viewing email'. It's a great tool in the marketing email analytics section, and would like to be able to pull lists based on that behaviour. 

[Paul_Rose]

It would also be really useful as a filter / property in Workflows

[SScott13]

It would also be very beneficial to include "time spent viewing email" info in reporting.

[MFrazier]

I would also like this data point for custom Scores.