What is a polite way to respond to a nosy person who acts smiley and friendly when they ask their nosy questions?

Here is just one example: i have a coworker who is not known for being particularly friendly. i don’t talk to her about anything except superficial issues, such as the weather, or whatever. Today she was asking me about my time (meaning my schedule), saying she notices i am late a lot. I am late a lot, and when i am, i charge it against my time balances (meaning, if i am 15 minutes late, i use 15 minutes of my vacation time). My supervisor is aware of it and she does not mind, because if anybody is late in our unit we use our own time, nothing is “given” to us. The supervisor knows that issues arise with traffic, children, cars, and as long as you “charge” your time, it’s your time to use/lose. my time does not concern my coworker in any way. She and I do not do the same work, she is not over me, etc. So she was asking me what time i leave at the end of the day, saying she notices i am late a lot. She was telling me about someone she knows who has children and is never late, wakes up early, etc. So while she was asking me these nosy questions, and smiling nicely while she did it, i was wondering how i could or should respond in a way that would not be overtly rude, but would let her know that i don’t think this is any of her business.

That’s just one example. In general: How would you respond to someone who is asking nosy questions, if you wanted to keep your response polite, yet letting them know you are not a pushover, and respond in such a way that they would think twice about prying any more?