There are different ways to display time, date, date_time fields in a rails app:

<%= form.time_select :published_at %>
<%= form.time_field :published_at %>

<%= form.date_select :published_at %>
<%= form.date_field :published_at %>

<%= form.datetime_select :published_at %>
<%= form.datetime_field :published_at %>

Safari view: safari datetime select

Firefox view: firefox datetime select

I like the *_field much more than *_select variants in this case.

My inital tweet about this