Can you provide more info? What youre asking is straightforward to achieve in ReadyAPI!, so we'll need more info to work out the problem.
You say you cant generate the query parm date values but why not? What is actually happening when you try? What does the logging indicate? What mechanism are you using for the property expansion? Where are you sourcing the date values from? Screenshots?
The more, concise info you provide the quicker someone will be able to respond with the solution.