Can i take advil (ibuprofen) pm, about six hours after taking excedrin extra strength?

Yes but only if ...: Advil is a brand of ibuprofen while Excedrin is a branded combination of aspirin, acetaminophen & caffeine, assuming that I'm describing your version. If so, you can take these two meds 6hrs apart as you asked. However, do consider taking plain acetaminophen rather than Excedrin in order to avoid having high(er) dose aspirin in your system along w/ibuprofen.