MtGox api - keeping track of bids/asks that get cancelled
Your link to the "old version of the API" is actually going to the streaming API which is still available.  Only the http version was updated and from there it looks difficult to obtain accurate  depth info reliably for precise time periods.

So I'd stick with streaming. Updated much more in real-time for your requirements.

Now they deprecated the depth:volume field but they still have volume_int, which is volume change * 1E8, so you could obtain volume from that:

//js for example
var volume = volume_int * Math.pow(10,-8);


Check out the github samples at the bottom of the wiki page to help get started.  For example, this one