There's different types of massages, including deep tissue. I'd get it from someone who knows what they are doing. The wrong massage or one too deep can ruin your taper.
Top swimmers (Olympic, NCAA) might have someone work on them every day if there is an injury or chronic problem. But for most swimmers, a good swedish massage or an easy sports massage would be appropriate two days to two weeks before. Probably just before you start the taper would be a good time too.
A light massage to energize and relax the muscles just before you swim can really help. Back in the 80's all the teams were doing it. I'm not sure if they are now...probably not. But again, you want someone who knows what they are doing. Going too hard and too deep can mess you up on a taper because your body is adapting.