99% of the descent clearances I receive are, "when ready descend ..."
0.8% of the descent clearances I receive are, "level change required, descend to be at xxx by yyy"
0.2% of the descent clearances I receive are, "descend to ..."
The last example is received so infrequently, it is always questioned just to make sure. I can't recall one example where I've been instructed to descend now.