This could be a solution.
date last question asked link: https://stackoverflow.com/questions/tagged?tagnames=ruby-on-rails&sort=newest&pagesize=1
date last question modified link: https://stackoverflow.com/questions/tagged?tagnames=ruby-on-rails&sort=active&pagesize=1
This response will be much shorter and you can isolate the date in "title" property of the first span tag inside the div class="user-action-time" tag.
I hope this helps.
<div class="user-action-time">asked <span title="2010-05-10 05:55:41Z"
<div class="excerpt">
I recently played with MongoDB in Rails using Mongoid. I like the ability to define attributes for models within the model file (as opposed to in migrations):
class Person
include Mongoid::Document
…
<div class="started">
<div class="user-info"><div class="user-action-time">asked <span title="2010-05-10 05:55:41Z" class="relativetime">13 mins ago</span></div><div class="user-gravatar32"><a href="/users/259900/kevin-sylvestre"><img src="http://www.gravatar.com/avatar/c78e40f8fc27a048f10ece6956a2fdf2?s=32&d=identicon&r=PG" height="32" width="32" alt=""></a></div><div class="user-details"><a href="/users/259900/kevin-sylvestre" >Kevin Sylvestre</a><br><span class="reputation-score" title="reputation score">743</span><span title="2 silver badges"><span class="badge2">●</span><span class="badgecount">2</span></span><span title="8 bronze badges"><span class="badge3">●</span><span class="badgecount">8</span></span></div></div>
</div>
<div class="tags t-ruby-on-rails">
<a href="/questions/tagged/ruby-on-rails" class="post-tag" title="show questions tagged 'ruby-on-rails'" rel="tag">ruby-on-rails</a>
</div>
</div>