When using liquid yeast, whether it be Wyeast or WL, you should always always always make a starter the day before. While the packs may say that it's enough to inoculate 5 gals of wort, that claim is pretty much hogwash.
The last time I used a liquid commercial yeast pack without a starter was my cranberry dubbel. A long time ago, in beer years (in real time....3 months ago) That was my learning experience. It was a new pack, and swelled plenty when smacked. I pitched it, and it took an excruciating 3 days to start. I actually went over to a local brewpub where I know the brewmaster, and got some yeast from him on the third day. By the time I got home, the Abbey yeast had finally started. The beer turned out fine with no infections and pretty good attenuation, but after that debacle, I make starters for all liquid yeast (exceptions are when racking directly onto an existing yeast cake, or when I get fresh yeast from that brewmaster I know). And I make big starters, too...a liter of water with 7oz of DME. Since then...very short lag times.