The max_tran in the library is usually a looser number than what we set design targets for, but will accept at signoff. For example, if the .lib has a max tran of 1ns, we might want to set the design max tran for 700ps (in the SDC file). But as we near tapeout, we might allow transitions between 700ps and 1ns. As for the clock transitions, those are usually tighter still, so in this basic example, we might set the clock transition to 500ps. Again, if you have a few sinks that don't quite make that transition, as long as it's within the library limit, you should be ok. I hope I've understood your question correctly!