Absolutely crazy system used by Vauxhall, I have the same problem on my 2017 Insignia VXR,but my 2019 BMW 740d stop/start system works within 5 mins of the engine being started even if the engine temp is still cold.
I guess if you want perfection you need to stick with the Germans, i was looking to part ex my VXR with a Vauxhall dealer who then offered me just over half of its value which i declined,so i guess thats my punishment for not buying German............... wont be making that mistake again