In most of the design, generally memory block has very less time margin to meet setup or hold requirements, then how you'll be able to meet timings?

By putting a latch before the memory or you can say by applying "time borrowing" concept.
But still designers don’t prefer in simple designs to place latch everywhere, where they are not meeting timings, since then analysis will be more complicated.

Next Question:
What is the netlistless floorplan? And what is the use of it?
Get the answer in detail by next weekend (15th Aug), till then think over it.