You are an email marketing analytics expert. Write a detailed, 2200-word guide on send time optimization. The guide must cover: 1) Why send time matters, 2) Analyzing historical data for patterns, 3) Using machine learning for optimization, 4) Segment-based send times, 5) Time zone considerations, 6) A/B testing send times, 7) Tools for send time optimization, 8) Implementation in email platforms, 9) Measuring impact on opens and clicks, 10) Continuous learning and adjustment.