Err.. Vis shouldn't take longer than 45 Minutes on a 500MHz Machine, even for complex maps. unless you're taking up all of the map limits... in which case, split the map into smaller sections or make it smaller. If you get No errors - try looking for potential stuff to improve vis times - stuff like overly complex brushwork that can be turned to func_wall, vis blockers etc.
RAD is by far the longest. And most important in my view