A torsion spring replacement on a door from this period runs close to an hour: unwind the old spring with a winding bar, pull the worn cable drums if they're grooved, install the new spring sized to the door's weight, and cycle it a dozen times checking balance. Extension spring jobs take about the same time but need the safety cables run correctly if the house doesn't already have them - that's not optional work, it's what keeps a broken spring from becoming a projectile.
Because the crew comes from Richmond, 18 miles out, we schedule East Bernard calls rather than promise a same-hour arrival. If the part needed is one we stock, the repair itself is done in a single visit once we're on site.