This cannot be accomplished with the min-max feature (as far as I can tell, anyway!), but could be accomplished with a skip feature.

In the Time column, create a skip feature. If a RT response is over 600ms, skip to a row with a 1000ms delay, then a presentation of the "Too slow" message. Adequate responses will skip to the next trial.

What you're basically doing here is making a manual min-max feature. It will make for a more complex input file, you'll have to make sure a lot of skips are going to the right place, but it will accomplish what you're asking for.