Change the updated timestamp for users
Here is an idea about running this in a more efficient way:

&lt;?php
  $loaded_user = user_load($uid);
  $user-&gt;changed' = time();

  field_attach_update('user', $user);
?&gt;


I am not 100% sure if this is gonna work for your setup the way you want to, i.e. if the hook you implement in your module is going to be called (not enough information there).

Let me know and I can give you an updated answer.

Cheers