In the meantime while they are pondering your request, you can always just post a GENERAL timeline of availability. For example, say something like the following:
Normally when I'm working it's:
Monday-Wednesday: noon-6pm
Thursday: 8am-9pm
Friday-Sunday: noon-midnight
Those are the hours I generally am available on those days,
but PLEASE contact me for current availability the day of your choice
by phone, PM, or email and I will let you know what's available.
You can also try maybe 3 other things:
1). Get a calendar on a web site that you can update DAILY. Mention in your ads for them to CHECK YOUR Current Availability on your WEB SITE CALENDAR (and perhaps provide a direct link to that)
or
2). Update your DAILY availability on your SHOWCASE every morning. It might seem like a hassle at first, but it will soon become routine and easy. Mention in your ads to LOOK AT YOUR SHOWCASE BIOGRAPHY for Current Daily Availability.
or
3). Put your DAILY availability in your SIGNATURE LINE.