A long-term time horizon can be your greatest advantage when investing in AI stocks.For three consecutive years, the S&P 500 (^GSPC +0.02%) has grown faster than average corporate earnings, with the index gaining 16.4% in 2025, 23.3% in 2024, and 24.2% in 2023.Based on metrics like its price-to-earnings (P/E) ratio and forward P/E, the S&P 500 is trading at a bit of a premium. The index's forward P/E of 22.1 tops both its five-year moving average of 21.15 and its 10-year moving average of 20.3.But the S&P 5 ...