If you exceed max journey time would depend on how it is set, if you touched in, train was about to go, got to Heathrow Island platform, and a train back to Ealing was just about to go, then you might get there quicker than if you touched in having just missed a train, next direct train to Ealing was few minutes late departing etc.
In both cases could exit about 40 minutes later (maybe more if you stopped at station toilet etc) which makes setting the maximum journey time quite difficult.
There are actually quite a lot of places within the oyster network where getting a fast train beyond, then going back station or 2 is quicker than waiting for next direct stopping train which may leave later (but pay-as-you-go would never pick up the extra section if it is retraced before touching out). If this extra is moral is another debate, but is a a consequence of having zones that can be reached faster.