Waveform narrowing is an attractive framework for circuit delay verification as it can handle different delay models and component delay correlation efficiently. The method can give false negative results because it relies on local consistency techniques. We present two methods to reduce this pessimism: 1) global timing implications and necessary assignments, and 2) a case analysis procedure that finds a test vector that violates the timing check or proves that no violation is possible. Under floating-mode, global implications eliminate timing check violation without case analysis in the c1908 benchmark, while for a tighter requirement case analysis finds a test vector after only 5 backtracks.