Well, I am able to leave a message any time.

I have called her on a holiday but by accident when at midnight I dialed her cell instead of the office number where she has voice mail. oops!!

She wants me to call her at any time. And she allows me to decide if I need to speak to her immediately and therefore call her cell. I haven't called her cell intentionally because it seems like a safety net and I don't want to lose it. But I would use it if I felt I needed to.