this is what you can do

1. transfer from stock fund to money market fund when you think the stock market is high and will go lower

2. transfer from money market fund to stock fund when you think the stock market is low and will go higher.

however, you have these issues:

1. it's difficult to time the market. you may end up selling low and buying high

2. many funds have short term trading fees. check out the fee before doing this.