External Memory Interfaces clock Critical Warning

TimeQuest can properly analyze transfers between different clock tree types, and I see it done all the time. I think this is a message from the IP you're using(a memory controller?). The ports it's talking about are all outputs, so I believe it's saying it can meet your requirements if all the outputs are on the same clock tree type(i.e. they will all have about the same delay). They may not be doing true static timing analysis between these I/O, and just saying that as long as it's layed out correctly, we know it works.