Better-than-nothing workouts

Hi, everyone, I work full time and have a baby at home and so getting to my masters practices has become impossible. I don't want to stop swimming, so I am going to try going at lunch, which only gives me about 30 minutes to swim. Not enough to be in great shape or really improve, but better than nothing, right? Does anyone have any suggestions or ideas for the best types of workouts to do when you only have half an hour? Btw, I am a mid-level masters swimmer who used to swim 90 minute 4,000-yard-ish workouts 4 days a week pre-baby if that makes any difference. Thanks in advance! And any other moms of babies or young toddlers out there?