PHP for alt tag

Hi,

I have a template with this code;

<?php while(have_posts()): the_post(); ?>
		  <a href="<?php colabs_image('link=url'); ?>" rel="lightbox"><?php colabs_image('width=157&height=157&link=img'); ?></a>
		  <?php echo '<div class="time">
						<p class="entry-time">
							<i class="icon-time"></i>
							<span>'.get_the_date().'</span>
						</p>
					  </div>'; ?>
		  <?php endwhile; ?>

I’d like to change the image’s date published being shown to the image’s alt tag via the small piece of code – <span>’.get_the_date().'</span>

i’ve tried all sorts inc; $alt_text = get_post_meta($img_id , ‘_wp_attachment_image_alt’, true); etc etc
NO LUCK!
can anyone help?
many thanks in advance