This strategy is exactly how it sounds - you see a gap up and look at the high point of the first 30 mins. You then buy any break out of that high point after the first 30 mins. You can confirm the breakout by using market internals, such as the VIX, TRIN or TICK. Look at this graph

More in depth information can be found on this strategy by it's creator, SandP500 Analyst - www.sandp500analyst.com.