Get messages from certain date range

Hi there.

I'm getting start and end dates dynamically from the current url (so admins can choose their own dates):

?startDate=2016-01-01&endDate=2016-02-15

<#assign dateStart = http.request.parameters.name.get("startDate", "")?string />
<#assign dateEnd = http.request.parameters.name.get("endDate", "")?string />

Now I'm trying to use these dates to get messages within that range, but I can't seem to get it to work.

SELECT count(*) FROM messages WHERE author.id = '${user.id}' AND post_time > '${dateStart}' AND post_time < '${dateEnd}'

I've been reading about different (iso) formats, converting with certain ?string variables, but I just seem to be stuck. Freemarker and dates are my biggest weakness.

Help?