Proper asset allocation based on age / time to retirement ----- yes.

Market timing ------ no.

How far away ar you from retirement? If it is more than 10 years, I would not worry at all.

We have quarter to half in bonds I don't trust the stock market

PP is correct ... You can't time the market and if you're asking advice on what to do if there's a correction, you really shouldn't be trying to get too cute. That said, it's not crazy to expect some sort of pullback or at least a stall after recent run up. Bonds are expensive but they still hold up when stocks fall and offer some downside protection. Value stocks are a better bet than growth if we stall out. Emerging markets are fairly cheap and haven't experienced nearly the same run up as the US.

You shouldn't do anything. You can't time the market.

What should you be doing if you expect a market correction and end to this 5 year bull run, in your 401k? bonds seem too expensive