Is it enough to be in range when the ability is activated in the hero phase to get those extra attacks? Or does the model need to be in range in the fight phase when it is making the attacks?
The text says it's activated in the Hero phase until your next Hero phase but it specifically says "whenever a SAURUS HERO within 20" attacks in the combat phase" so I would say in the combat phase.
EDIT: I am an idiot who confuses Carnosaurs with Cold Ones. The below post might still be interesting so I'll keep it nonetheless. For the ScarVet on Cold One you are right, his ability works in the same way as the one from the Oldblood. ------------------------------------------------------ Original post, talking about Carnosaurs: It is a bit different. The ability says you buff a single unit within the 15" range (it is used in the hero phase, like all command abilities that don't say otherwise), and then it lasts until your next hero phase, without specifiying a phase it works in, or a range. So it would work in the shooting phase, it would work on ranged weapons (although the only ranged weapon on a Saurus is an Oldblood on Carnosaur's Sunbolt Gauntlet), and it would work if the unit went out of range in the meantime. Also note that fluff-wise the Oldblood's command ability is his presence near the affected heroes that makes them fight harder. So it is clear that once they move away they don't have the buff anymore. The Scar-Veteran's buff is a bit different. It is targeted on one unit. He roars at them and that inspires them for a while to fight harder, regardless of whether he walks away or not.