I have some kolsch II yeast I got from NB on my last order, its use by date is march 28 2013, I found out tonight, so I popped the wyeast pack and am hoping for the best, here is the question if it blows up like it should is the yeast still viable, second if the pack blows up how long should I keep it before I have to use the pack, its going to be two weeks before I have a chance to brew, I popped the wyeast in a panic probably not a great choice thanks for the help
Are you making a yeast starter at all, or just smacking the pack? I would recommend a yeast starter for sure, since you won’t be brewing for a couple more weeks yet, and since the yeast is getting kind of old.
It’s actually kind of a good thing you smacked the pack already. If the yeast pack blows up quickly, I think you can refrigerate it and then make a starter a day or two ahead of time. If, on the other hand, it takes like a whole week for the pack to pressurize, then you might want to make your starter earlier, maybe 3-4 days in advance, to give your yeast a little better head start.
I would make a starter 1 week prior to the brew date. This give you 4-5 days for it to ferment (no stir plate) and 2-3 days in the fridge for the yeast to drop.
First of all, remember that Wyeast does not have a “use by date” on the package. The date shown is the date of packaging. The general rule of thumb if you are not going to make a starter is to smack the nutrient pouch ahead of brewing a day for each month past the packaging date. In your case that would be two days prior to brewing. In your current situation, just put the package in the fridge and take it out and let it come up to room temp a day or two prior to brewing and you will be fine. This is of course assuming you are not making a starter. Your Wyeast packages, properly kept cold, will be fine 6 months after the packaging date imprinted on the front and many may still be good much longer after that. Although once the package moves into six months and beyond you should always make a starter with it as the viability of the yeast drops to the point to where you will need to grow more yeast for your proper pitching rate. Remember, one smack pack with no starter is really only optimal for a 19 L batch at 1.045 and less. Put your package in the fridge and you will be fine to brew in 2 to tw2-1/2 weeks. 
thanks a lot guys for all the helpful responses in about two hours after original post the bag had blown up, thanks again for all the help
