Advanced process technologies impose more significant challenges especially when manufactured circuits exhibit substantial process variations. Consideration of process variations becomes critical to ensure high parametric timing yield. During the design stage, fast estimation of the achievable buffered delay can navigate more accurate and efficient wire planning and timing analysis in floorplanning or global routing. In this paper, we derive approximated first-order canonical forms for buffered delay estimation which considers the effect of process variations and the presence of buffer blockages. We empirically show that an existing deterministic delay estimation method is over-pessimistic and thus result in unnecessary design rollback. The experimental results also show that our method can estimate buffered delay with 4% average error but achieve up to 149 times speedup when compared to a state-of-the-art statistical buffer insertion method.