I have told people, "Hey, call or text any time, but I might not be able to get back to you that same day." It's totally cool to not make an offer, or to make a narrow offer with really clear boundaries around it.
Le he dicho a la gente, "¡Llama o escríbeme a cualquier hora, pero puede que no sea capaz de responderte el mismo día!" Está totalmente bien no ofrecer algo, u ofrecer algo con limites claros.