one other tip -- although it may not be so useful for your particular situation because you already have decided to take a much earlier flight, and there are not that many options from DTW:

You can sometimes tell if your flight will be delayed (so that you can prepare to ask for irregular ops accommodation) by the incoming aircraft's status. For example, Monday May 12th's DTW-IAD flights were all delayed, and you could have predicted it by looking at the inbound IAD-DTW flights that delays were stacking up.

this is useful when this knowledge gives you other options to get you out in the meantime, but as I say, at DTW, it does not help too much. Although, it would help if you were planning on taking the 7:15pm flight, saw that it was delayed, and could ask to be put on the LH codeshare or ORD-FRA flight.

see here for example:

Flight 7288
Detroit, MI (DTW) Mon, May 12
Scheduled: 6:05 AM
Actual: 6:49 AM
Washington, DC (IAD) Mon, May 12
Scheduled: 7:32 AM
Actual: 8:28 AM

Flight 7207
Detroit, MI (DTW) Mon, May 12
Scheduled: 12:05 PM
Actual: 3:15 PM
Washington, DC (IAD) Mon, May 12
Scheduled: 1:32 PM
Actual: 4:59 PM

Flight 8056
Detroit, MI (DTW) Mon, May 12
Scheduled: 7:15 PM
Actual: 8:15 PM
Washington, DC (IAD) Mon, May 12
Scheduled: 8:44 PM
Actual: 9:45 PM


and the corresponding delayed inbound flights:
Flight 7207
Washington, DC (IAD) Mon, May 12
Scheduled: 8:57 AM
Actual: 1:15 PM
Detroit, MI (DTW) Mon, May 12
Scheduled: 10:29 AM
Actual: 2:43 PM

Flight 8056
Washington, DC (IAD) Mon, May 12
Scheduled: 5:06 PM
Actual: 5:25 PM
Detroit, MI (DTW) Mon, May 12
Scheduled: 6:43 PM
Actual: 7:31 PM