Quartus_map long runtime with no messages

How big is the design? Create sub-projects on major hierarchies and synthesize them. Not perfect, but should help you narrow it down. Even then, it may be difficult to determine. Synthesis probably doesn't report detailed run-times because it's usually a small(ish) portion of the full compile, and so not many people ask for it.

One other thing would be to create partitions on the design and set them to post-synthesis. This will synthesize each hierarchy independently. More importantly, as you make changes, only the necessary hierarchies will be resynthesized. (Quartus gives messages on how long each one took, but last I checked, they weren't very readable.) Be careful to monitor the size of the design though. Partitions prevent synthesis across boundaries, which can make things grow in size, especially if you were tying off inputs to logic expecting it to get synthesized out. THe quartus II handbook talks about this in recommendations for incremental compilation.