Originally Posted by
flyerfirsts
I don't mean to say predict in advance, but to be standby on the other one and only switch if I clear.
If you're standby, you can't be upgraded. Only confirmed passengers are eligible for the upgrade list, and GAs generally process the upgrade list at the gate before they clear the standby list.
You can try to SDC (not SDS) at T-24 if you haven't been upgraded and the other flight looks more promising, but I wouldn't expect the odds of a PM being upgraded into a (domestic) flat bed seat at T-5 days to be high. Switching flights also means that you reset time of upgrade request (the final tiebreakers for upgrades).