Multiple filed handlers in Views for a field
You don't. That's not possible.

But you still have options:


Define your own field handler and add support for multiple display formats using configuration options, have a look at this snippet for an example: https://gist.github.com/juampy72/5816530. The key methods to implement this are option_definition, options_form, options_submit and render.
This is more of a work-around. Copy the definition of the first field handler under different database column key, e.g. $data['history']['timestamp_as_date'] = array( .... Then implement your own filter class as before, but also override the query method in order to ensure that the timestamp column is present. Then display that as you like.


There are a lot of code examples out there.