OP is not speaking of being "bumped." He is asking about the consequences of failing to show up for his ticketed flight and then not making it off standby for the later flight. The simple answer is that if you standby and do not make it onto that 7:00 PM flight, you will keep rolling over on standby until a seat opens up on some flight. Depending on routing, that might be tomorrow.

I strongly advise against standing by for a later flight or your are entirely flexible. Particularly on a Sunday evening at a time when air traffic is returning at warp speed. The lack of positive space with no status puts you in a tough spot.

Take a look at outright changes -- which might include different routings. Perhaps there is something to be had. With no change fees, always possible that the fare difference is smallish.