In practical terms you should turn the shortest way back to the overhead and commence the MAP for the Instrument RWY you arrived on. HOWEVER, some airfields publish quite specific procedures for losing visual on a circling approach, quite often necessitating continuing the circle and the carrying out the MAP for that runway, not usually if a reciprocal is in use admittedly. If that is the case then a bit of guesswork and a stopwatch might find you a gap!!!! Did I just say that????
