In A320 family the max brake temprature for take off (with brake fans off) is 300 degrees.
The only SOP that Airbus has on the brake fan use is after landing (five minutes or gate or 300 degrees which ever happens earlier).
In my company there is no SOP for brake fan use while taxiing out or before take off. Most captains I have flown with like to keep the temprature below 100 degrees, so as the temprature is approaching 100 degrees we turn the brake fans on. Some ex-pats I have flown with do not like to use the brake fans as much. The only time we have kept the LG down was when the brake fan was MEL and the temprature was reaching 200 degrees just before take off.