Business phone calls should be returned within the same business day unless advised otherwise.
If you know you will be in a meeting all day or you are working off site for the day and will not have access to your voice messages, leave an announcement telling the caller when they can expect your return call.
My office message may sound like this if I’m in an all day training seminar:
“Hello, you’ve reached the Etiquette School of Ohio and the office of Sandy Hyde. I will be working off site all day Wednesday, October 24. Please leave a message and I will return your call the morning of Thursday, October 25.”
If you are on vacation, it is helpful to the caller if you leave the name and number of someone who may help them in your absence.