I would guess about 40 minutes to an hour.
Related story: my band opened for Dream Theater in the 90's. John Myung and Petruci were each in different back rooms warming up, runnings scales for about an hour. I remember thinking, well yeah that makes sense, otherwise they won't be able to nail all that mad complex stuff right out the gate.
Ok so I'm not alone then! I remember reading Flea has a very long warm-up, including running around with his bass on
