Guys need to stop making these women into bosses and stop being the 'sidepiece'. You shouldn't be worried about the perfect time to call her. She should be worried about being by the phone to receive your call when you call her. A lot of men are stuck in the zone where they are dealing with unscrupulous women who are talking to multiple guys at once, so she feels that any one man's particular attention, unless he is on that other level, isn't worth much.
If you call a broad at a decent hour and she doesn't pick up, you're in that pile of negroes who are there for entertainment and who get ignored when she sees fit. Why reward that kind of broad with any of your time or attention, which is precious? As a man with a boss mentality, you shouldn't be tip-toeing around women. They should be eagerly awaiting for your call, and if she isn't, you need to move on to another woman who is. NEVER undervalue yourself when it comes to these women. If she isn't making herself easy to deal with by being cordial and easy to access, then she doesn't value you. Move on.