What time of day is best to text a girl?

There's this girl I really really like a lot. We used to be a couple, but she needed space. It's been months since the breakup, but now she's suddenly reappeared in my life. One of our close mutual friends told me my ex doesn't know if she wants to go out with me again, but she does really want to start talking to me again. Our friend told me to text the girl Sunday (which is today). What time should I text her, so she's not likely to be busy, and what should I say?