Well it's done! I let each of them out in turn for a short while. I'm satisfied when they immediately find their way back to the catflap. Then I know that they can find their way. Unfortunately my garden is at the back and the catflap is at the front (can't put a catflap at the back). But we live on a cul-de-sac, and it's quiet and green at the front too, although entirely open.
Shanti was first out. She marked a bit, then went under my car, then wandered into next door but one's garden. Then something spooked her and she made a dash for it straight back to the catflap, and straight in. She's asking to go out again now!
Meesha went out next. She's my little homebody, but she was actually the bravest and went the furthest, disappearing out of sight to emerge a few minutes later on a nearby roof! She came back when called, although she needed at bit of coaxing to give up her new-found freedom and go back indoors. Meesh was out for about half-an-hour.
To my surprise, Sabby, who loves the great outdoors, seemed reluctant to go out at all, although he is very cautious. I had to coax him out! He marked everything close to the door, and then got spooked about everything, dashed next door, then dashed back again, and straight in through the catflap!
Well that's the hardest part over and done with. Phew! Tomorrow I'll let them out for longer, and all three at the same time. Then on Monday it will be business as usual, with all-day access to outside for them.