I've found that checking their website is a good place to start. Most providers will list their general hours or availability there.  
Also, you need to give them 2 or 3 days sometimes to get back to you when you contact them.

Some ladies have a job and escort only part time.

Some ladies have children to get off to school and then get ready while others may go to the gym.

Still other ladies may strictly work days or evenings.

I think you have an idea of why each ladies schedule is different.

Always check the ladies website and read everything before asking a question..I know I love to see a man who has taken the time to get to know everything he can about me ahead of time.

Kisses Haley

If you're truly new to the hobby, you're probably better off making initial contact 3-5 days before a desired appointment. It can take 24-36 hours for a busy escort to get back to you. (And I don't just mean busy with escort work. She might have another job, kids, etc.)  Additionally, you only want to connect with providers who do some sort of screening. It is hard to be screened in a few hours although some definitely do it.

Just my perspective. Other's, I'm sure, have different experiences.

and seeing as you're trying to reach one at 7:45am you should be focusing on the early birds.

Most pros tend not to pick up their phone til after 9am. If you're specifically seeking early morning appointments you'll either need to book your appointment in advance, or shop at craigslist which is usually repleat with gals advertising (realtime) at any given time of the day. Craigslist however is more often occupied with far more flakes than "pros".

Some of us DO have a life outside of Providing meaning we have full time jobs and careers  I for example am a Nurse and i only Provide in the evenings and on the weekends, and thru out the course of the day i only can get back to who ever calls my hobby phone at certain times and limited times during the day as well.
All the important info should be in their websites as to how to get in touch and their hours of operation and if the one you want doesn't answer, just leave your message, if she does the right thing she WILL call you back to you and if she doesn't, there are literally thousands to pick from that will show you the respect and the courtsey you deserve and get back in touch with you to set something up..but remember if you call in on a PRIVATE NUMBER or a Blocked Number thats a sure way of not getting a response back! Keep that in mind!
Jay

If you want to see a lady for a morning appointment, you need to set the appointment at least the day before.  These ladies have more to their life than sitting by the phone at 8 a.m. waiting for you to call.  They also need time to screen you.