Paginate Entries by Day
Instead of using pagination, you might try creating a custom route using tags for year/month/day. Those tags will be available as variables in the template that you can use to load that days entries and generate the nav for next/previous day, etc. Using ajax the uri won't be visible to the user anyway.

{% set postDate = year ~ '-' ~ month ~ '-' ~ day %}
{% set nextDate = postdate|date_modify('+1 day')) %}
{% set previousDate = postdate|date_modify('-1 day')) %}

{% set entries = craft.entries.postDate('and', '&gt;= ' ~ postdate, '&lt; ' ~ nextDate %}

{% for entry in entries %}
    {{ entry.title }}
    ...
{% endfor %}

&lt;div class="pagination"&gt;
    &lt;a href="{{ 'section/' ~ nextDate|date("Y/m/d") }}"&gt;next&lt;/a&gt;
    &lt;a href="{{ 'section/' ~ previousDate|date("Y/m/d") }} "&gt;previous&lt;/a&gt;
&lt;/div&gt;


Not tested, but should be close. You'll need to modify the links to work with your ajax of course.