About a day for us.
It's pretty sturdy in the fridge.
A touch of baking soda in tea rounds out the tannins in iced tea. Just a pinch. Will soften it--especially if you have hard lime water in your area.

Thanks. Was hoping for longer, though!

I make and consume iced tea all summer long and try to make the amount we will consume in about 3 or 4 days. Beyond that time it starts to taste "stale".

If you keep the tea refrigerated the 3 - 4 days sounds right. I have had iced tea served to me in restaurants that has the off taste of mold. I assume that means it's not kept in the fridge and/or kept too long. I prefer making it with boiling water to steep, but you can put water and tea in the fridge for cold brewing -- that may have an edge on keeping time.
This is a cold drink recipe with a tea/syrup base. The syrup will keep a long time (refrigerated). If you want a longer keeping period than you get for standard steeped tea, you could use this as a model for a concentrate, then add as you wish. I've really enjoyed it -- http://www.food52.com/recipes...

3 or 4 days in fridge should be ok

Thank you everyone for your opinions!

I never leave tea overnight. To me, it loses the snappy astringent-ness and just tastes flat.