Over the past 2 years, the S&P has crossed the 50 day MA 10 times*. The average length below has been 42 days; avg above has been 100 days.

Currently the S&P is 68 days above the 50 day MA, which is getting close to the average of 100 days above in most cycles.

*=10 times above is based on significant movements greater than 20 days. The calculations were done very quickly and there could be some mistakes. This is not financial advice but I would sell sooner than later.