How to filter nodes using timestamps?

I am trying to create a view to return nodes where the changed field (i.e. last modified date) is greater than or equal to a given value. For simplicity reasons I'd like to use unix timestamps to pass data between the view (on the server) and the client (a mobile app).

So far I've tried using both a filter and a contextual filter, using either the [node:changed] field directly or the [date:node] more generic filter/contextual filter but without any success.

Any hint on how to achieve my goal? If not using timestamps passing data according to ISO-8601 could be a viable option, but I need seconds granularity. Also, the [node:changed] is already part of the view as a timestamp value.