When do you start becoming conservative with 529 accounts?

My oldest is in 6th grade. Currently have her in a mix of large/mid/small cap and total stock market. All Vanguard funds. I have coworkers who lost significant gains 2008-2009 when their kids entered college. I'm very weary of the current financial status and economic outlook of the country. Should I just continue and don't look at it until another 3-4 years, or start moving these funds into bonds/cash/value? 529 accounts are a little trickier with a shorter timeline in the market.