Unfortunately, focusing is not possible with the iPad. The only way the focus will be placed in the desired field is when the user ‘clicks’ on the desired field.
Update 2015-01-08:
As explained in this answer by Matt:
…
iOS will only allow focus to be triggered on other elements, from
within a function, if the first function in the call stack was
triggered by a non-programmatic event. In your case, the call to
setTimeout starts a new call stack, and the security mechanism kicks
in to prevent you from setting focus on the input.