This isn't about sympathy it's about clarity, you're of the opinion that a person should make assumptions based on what time of day they receive a phone call and my opinion is that being straightforward removes all doubt, confusion or need for assumptions.
Some women will be turned off by it, that's the entire point, you don't have to waste your time with those women, some women won't be turned off by it and those are the women you proceed with because you both want the exact same thing, no games have to be played, there's no room for her to ask "what are we" because you've made it clear up front, you didn't have to lead her on and make her think the situation could become something more than what it is.