Old slurry vs. starter vs. Mr Malty

So I washed some W-1028 recently and it's been in the fridge for about 2 months now. A few days ago, I pitched about 500 ml of it in a 5.25 gallon of 1.057 wort as per Mr. Malty calculator. I did not make I starter because I was under the impression that the Mr. Malty "Repitching from slurry" equations do not necessitate one. Now here I am 72 hours later and no action at all. I have another 500 ml that I could use so...

1. Should I make a starter, much as the same way as I always do with an original Wyeast smack pack? About 1.5 liters?

2. Should I wait out the 2-3 days or pitch at peak activity (assuming that I get some) 12 some odd hours later?

You should have made a starter with the washed yeast.

Stored yeast, washed or not, loses viability the longer it's stored. In the case of unwashed slurry, a good estimate is 25% loss per seven days stored. In other words, after a month it's pretty well shot. Washed yeast does better than that, but I don't have those numbers before me.

Before you do anything, take a gravity. You may have some activity. Hell, the improbable may have occurred and the ferment went by so fast you didn't even see it.

If the gravity is unchanged or little changed from the OG, I'd get some more yeast in there pronto. Frankly, I don't think you've got time to wait for a starter to get going. Hie thee to thy LHBS and get a packet of an appropriate dry yeast and get it going if necessary.

Bob