Conditional DCA

I've been selling off many of my good earners lately in favor of some ETF's. I'd like to get into the ETF's with a strategy along the lines of every day at 3:45 PM, if the market price is lower than the previous day close, purchase $500. Is there a platform that can do a conditional like this? I think the specific time is the feature that I can't seem to find.

Thanks!