When does next weekend become this weekend?

On a Friday you would say 'this weekend' referring to the next 2 days and 'next weekend' would be over a week away. On the Saturday and Sunday 'this weekend' would mean those two days and 'next weekend' would be a week away.

On a Monday 'this weekend' could still mean 'this weekend [just gone]' and 'next weekend' could be now less than a week away. The weekend after that is 'the weekend after next'.

At some point in the week it changes and the weekends all shuffle along. 'This weekend [just gone]' becomes 'last weekend'. 'next weekend' becomes 'this weekend' and 'the weekend after next' becomes 'next weekend'.

What I want to know is when does it change? Is that somewhere on a Wednesday? If so, when? At Midday (GMT) on a Wednesday what would 'this weekend' refer to?

Just asking.