Hyphen in the noun 'switching-off'? Or gerunds of compound verbs, more generally?

I believe it should be written without the hyphen.

In the case of a noun + gerund, whether or not a hyphen is used depends on if the phrase is adjectival or if it is acting as a noun.

The company's decision making was met with criticism.

vs

Their decision-making process was not regulated well.

Since "switching-off" is used as a noun, it should instead be written as "switching off".

Source: Department of Justice

The style guide used by The Economist (quoted here) suggests that hyphenation be used to avoid ambiguities.

If "switching off" in a sentence introduces an ambiguity, it can't hurt to use it.

Here is an example with no ambiguity:

Switching off the light would be a good idea now.

Here is one with some ambiguity:

I think your switching off of the light would be a good idea now.

Most likely you are suggesting that someone turn the light off, but switching could conceivably mean something else not associated with the preposition following.

The meaning is clear with a hyphen:

I think your switching-off of the light would be a good idea now.