Probably lots of views on this one but my current ways of doing things are:
If it is a brand new wyeast I smack it 1 week before brew day and make a 2L starter once it swells this gets divided amongst 6 stubbies after fermentation looks to be complete (shake (careful!) and pour).
From a stubbie starter if I am organised I get it going in 1.5L of starter about 48-24hrs before brew day. Hopefully on brew day I have seen signs of action in the starter. Varies, sometimes a good Krausen, mostly I can see the bubbles rising in it like a carbonated beer and up to 1cm of yeast sitting on the bottom. Ideally I would say allow two days before brew day to get the starter going.
I always taste a small amount before pitching, if it is putrid it goes in the bin.
Something to heed when reusing liquid yeast. Always taste test your yeast before pitching into a brew. You will know if it is off.
I have had starters last over 12 months. I recently threw out a 1056 which I had used about 4 times but it was about 18 months old. And I dont split my yeast into stubbies. I make a 2 to 3 litre starter and decant half off and place in fridge in a single bottle.