Wordpress - How to get date for each post?

I ran into the same problem several times, following changes worked for me in the past:

while (have_posts()) : the_post();
//some html
<li class="icon-date"><?php echo get_the_date( 'Y-m-d' ); ?></li>
<li class="icon-time"><?php the_time( 'H:i:s' ); ?></li>

Instead of the_date(), use get_the_date().
The only thing to be aware of, is that values returned by get_the_date() have to be echoed.

Looking at the Codex page there is a special note about the_date().

When there are multiple posts on a page published under the SAME DAY, the_date() only displays the date for the first post (that is, the first instance of the_date()). To repeat the date for posts published under the same day, you should use the Template Tag the_time() or get_the_date() (since 3.0) with a date-specific format string.

Also, If you want to control the format in wich get_the_date() is returned in Admin, you can use get_option('date_format'). This way if you change the date format in the Admin, these changes will me made in your code too.

while (have_posts()) : the_post();
//some html
<li class="icon-date"><?php echo get_the_date( get_option('date_format') ); ?></li>
<li class="icon-time"><?php the_time( 'H:i:s' ); ?></li>