Research why the Timer triggers the event earlier than it's configured (Approximately not earlier than on 15ms).

To solve this behavior we were needed to adopt the test asserting on:

stopwatch.Elapsed.Should().BeGreaterOrEqualTo(minHeartbeatInterval - TimeSpan.FromMilliseconds(15));

instead of the original one:

stopwatch.Elapsed.Should().BeGreaterOrEqualTo(minHeartbeatInterval);