T1E Dependant VISA to Spouse VISA

Dear Members,

I have recently received my ILR via 10 years long residence route.

My wife is my T1 dependant. Her T1 dependant Visa expires in 2022.

I am not sure about when she needs to apply for a Spouse Visa.

I made a phone call to UKVI contact centre. A staff told me if the Home Office contacted my wife to curtail her T1 dependant Visa then she would need to apply for a Spouse Visa within 60 days of the curtailment. If the Home office doesn't curtail her Visa, she can wait before her T1E dependant Visa expired to apply for a Spouse Visa.

Could you please advise if that's true? And please kindly point me to the relevant guideline?

Many thanks

Dear members, your opinions are much appreciated