Almost instantly. Consider that most grids are designed to work in a way that power generation and consumption MUST always be equal.

This means that we constantly fine-tune the power output of power generation plants.

We loose this, we stop receiveing energy in our homes.

We would still be able to generate it, but our grid wouldn't be able to work with it.

This need will be compensated in the future with solid energy storage systems spread across the grid. Consider that the unpredicatability of renewables concurs in this balancing complexity.