Views rewrite results: div in anchor
If this was purely about just views accordian, then the rendering output you show would not be showing a div with a class of panel-heading. I see this as more likely about trying to have a views accordian rewrite into a panel and probably panels accordian at the same time and having the anchor tag reduced to a single line output when the html is stripped out. So without knowing what the full details are I can only suggest trying the rewrite as:

[field_event_date_1]
[title]

[field_time_slot_1]


or if only the div tags are being stripped out then try:

&lt;div class="session-date"&gt;[field_event_date_1]&lt;/div&gt;&lt;br/&gt;
&lt;div class="session-title"&gt;[title]&lt;/div&gt;&lt;br/&gt;
&lt;p&gt;&lt;div class="session-timeslot"&gt;[field_time_slot_1]&lt;/div&gt;&lt;/p&gt;