A general enquiry about an SPs working hours is often hard to answer as many girls don't work set hours, it will depend on the enquiries and bookings they get, we also get a lot of 'let me know when you are available ' or ' when are you working ' messages which when we reply never go further.
A more specific enquiry like above will or should definitely get better results, I personally have a line at the beginning of my profile that says something like, My diary is just a reflection of my availability, if there is nothing shown on their diary then a more detailed message would be beneficial.