I wrote the following sentence:
"Tell me when when you know." (Note the double "when".)
The intended meaning was that of: "tell me when you want me to be there, when you know when you want me to be there". I was then thinking: I feel like it would read a lot nicer if instead, I wrote "tell me when, when you know"; but my question is, is the comma there optional or necessary? In other words: is "tell me when when you know" grammatically correct without the comma?
As alternative examples where this is less bold (but which I think are the same in principle):
Let's say someone asks me to, say, run some software on their computer, and I want to ask them for instructions when they have a moment; so I say: "tell me how when you have a moment". As in, "tell me how to do it when you have a moment". Is a comma necessary here? ("Tell me how, when you have a moment.") Or is it just a matter of styling at this point?
And if so, then is that the same as the previous case, or is it different for some reason? (It seems to me to be the same case: if instead of asking for "how" I asked for "when", i.e: when I should run the software, then the question would be "tell me when when you have a moment," which brings us to a similar when-squared predicament.)