If you booked PDX--SEA--MSP--xxx leaving at like 10pm you'd have some flex...... standby for an afternoon PDX--MSP nonstop (which is what I imagine you want to do.

The airlines are pretty strict about the same-day thing, but I've stood by for earlier flights many, many times: with family in MSP and friends near DTW, I kill multiple birds with one stone on my transcons. Plus, now with the Mpls light rail, I can get to my mom's house a little quicker. Will try the light rail for the first time in 24 hours!!

Only once has an agent mentioned the 4 hour rule--- most don't really pay attention. In the past I've also had agents offer to put me on the standby list from MSP to my final destination, but I decline and tell them I want to support the MN economy at the Mall of America.