I do things like this sometimes - but typically not where the legs actually cross.

You are definitely taking a substantial risk in terms of, you know, actually getting to your destination. But it has - generally - always worked out for me.

I do not feel like you are breaking any rules by taking advantage of your standby privileges, but it may become a problem if you do a lot of A-B-A where the flights physically overlap. I'd be a lot more comfortable (and most of my examples are of doing it this way) with a straight turn A-B-A in the evening, or A-B-C all in the evening, and then I show up at the airport at A in the morning to standby onto the first A-B, thereby creating a full day of time in B (a "free" stopover).