This is good advice.But if you say no be prepared to say why the date is open on MOAS if you cant do it.
If you get a call at lunch time for a match the same evening (has happened to me once) and the answer is I would have been available if I had known yesterday, but I can't get away from work early enough at such short notice, no-one is going to be surprised or upset. If you take the call sat on a beach in Mykonos, expect something else !