SC
My recollection is that from ground idle to max power can take between 5 and 7 seconds, a little less from flight idle.
The spool up time is from idle to a point at which max thrust is available virtually instantaneously
Remember the AF A320 fly-by that ended up in the trees? Well, they set max thrust shortly before they reached the trees, and you can still here the thrust increasing as they hit the trees.
On the Airbus, approach idle is commanded by the FADEC system whenever the flaps are awat from 0, facilitating 'rapid' achievement of TO/GA thrust; however in the AF case they had overridden the autothrust and were at a height above ground where the logic said they were landing, so some of the autoflight functions were disabled.