180 day rule or 90 day Rule

[VWS]

Hi

My wife is on a Tier 1 Dependent visa (50k route). Her visa start date (1st extension) is from June 2019. She was outside UK for almost 2 months from Sep 19 till Nov 19.

She is flying again in the start of next month from March 20 till end of May 2020. (3 Months)

I am a bit confused about the rule.

Is it 180 days allowance for a rolling 12 month or is it 90 days?

if its 90 days then I ll get the return ticket date changed.

Kindly if someone can illuminate me on this please.

Thanks

[CR001]

There is NO 90 days rule.

It is 180 days in any 12 month period which breaks continuity of residence.