I agree that you cannot write a macro with 0.5s interval, but it is possible to wait fractional seconds within a macro. I regularly use a macro that waits 0.23s (just toggles XHBs, not activate actions). Each line in a macro has a wait time of [inverse fps] seconds. In theory, you can make a macro to activate two oGCDs with 0.5 interval between each, as long as the frame rate is under 28fps. It's not practical at all.