Exactly as described, this sets how much time elapses between the start of one repeated test group and the start of the next, for this profile. This is what turns a single test profile into a recurring soak test rather than a one-shot measurement, so a short interval on a long-duration profile means the circuit gets hammered with back-to-back test groups almost continuously, while a longer interval leaves gaps of idle time between test groups. For example, an interval of one hour with a 24-hour duration would run one test group every hour for a full day, producing 24 separate data points rather than one continuous measurement.