that is the correct procedure for standby, and it might be worth it to ask the check-in agent whether it will be necessary to tag your bags specially so they can be identified for standby. It might actually even be possible to do the standby if you check-in online the night before or even get the flight confirmed if the computer is feeling unpredictable.

The other thing is that by taking the 12:05 DTW-IAD flight, there are now three options for your IAD-FRA flight, (UA916, 5:16pm-7:10am; UA952, 6:51pm-9:10am; and UA932 your original flight, 9:48pm). You will have to decide whether you want to ask the agent to put you on standby for an earlier IAD-FRA flight too, because that will determine how your bag is tagged. It might not actually be a choice, given the loads on your day, and whether the agent wants to let you standby for an intl flight, but you should keep it in mind.

However, a final point I would also note is that (in addition to the advice given in your previous thread ), there now seems to be 2 Lufthansa codeshares nonstop from DTW-FRA on that day (see here) that would provide an additional useful backup plan so you don't have to fly to IAD 7 hours in advance. They must be a new schedule addition since the last time you asked this question. If anything appears wrong with your DTW-IAD flight, you would have a good chance of getting on either of those flights.

But for your peace of mind maybe you will want to go with your own plan.