Ambrose, whose only laps since March came in practice at Hidden Valley, clocked the eighth fastest time in the 30 minute session.
Ambrose ran a total of 15 laps, with six of his flyers in the low 1:11s.
His best of 1:11.12s proved just 0.6s from the pace in a session that saw all cars on pre-marked tyres.
“It feels really good,” said Ambrose post-session.
“My concern always seems to be brakes with these cars, I just can't get a feel for it.
“As I got going in that session I got better and better under brakes, but the tyres got worse and worse, so it kind of neutralised our gains.
“Overall I was pretty happy with the session.”
Ambrose said he was determined not to interrupt primary driver Scott Pye's preparation for the weekend, with the first full practice session starting just minutes after the co-driver run.
“You're mindful that Scott is just about to jump in the car, so you don't want to put it in the gravel trap and create extra work.
“You try and just look after the car and get some experience and that's what we're doing.
“It sounds weird (to need experience), but it's just the landscape and the way it is at the moment.
“It's a bit surreal to think you can come back and struggle to get back in the car and reacclimatise, but it is what is is and we're working through it.
“But it was a good session for us and we're really pleased.”