As datetime picker only has the changed event you can do the following
a) First give any default value through service which will be binded to Mashup Load Event
b) Then when the default value service is completed i.e ServiceInvokeCompleted you bind that to the SQL service you are now using on date time picker
Whole Scenerio below
We had the same problem. For us the best solution was to create a search context with an infotable.
The binding works well through the infotable even if the date picker is undefined.
That problem is cleaner to encapsulate the entire search form. As seen, it's safer.
It allow too to pass the context through mashup parameters correctly, that is not working well with simple datetime data type.
Using a default value in services was not a good solution in our case.