Which Date type is used in Dynamic SQL?

I am trying to use Dynamic SQL because I need to supply data at runtime.
The generated query returns 0 rows for some reason. If I copy/paste the query into Monitor, it works correctly. I am suspecting it has something to do with dates being the wrong format (I am supplying them in 'YYYY-MM-DD' format). Is that the cause? And if so, how do I supply dates in correct format?