If you are worried about lower prices then I'd consider a layering strategy. S&P off 15% from highs, add. S&P off 20%, add. S&P off 25%, add. So on and so forth. That's just an example as you can change it based on preference.
I wouldn't get caught trying to 'time' the market but I would be mindful that with a VIX over 50, 3-5% market fluctuations should be expected. If available, you can use buy limit orders to add cash to positions at pre-determined levels.
This helps alleviate some of the emotion behind investing when the markets are declining at this pace. It also helps alleviate chasing the market when it does rally.
After severe market sell-offs or the type of destructive trading we've seen, there is usually a lot of constructive trading that needs to take place prior to the resumption of normalcy and significantly higher prices. It's very common to see significant bounces, like we already have at times, when ultimately lower prices are still to come. V shape recoveries are possible (4th Qtr 2018), but so are W's. Most significant market pullbacks end with some sort of general price consolidation. In the event of a W, you get the market to hit the same general point more than once. If that were to occur and you have limits in at lower prices, you can always make those market orders. That's a better option that just going all in at one price, IMO.