5 cakes you can eat for when you're trying to gain weight.
Materials needed for when you build your time machine.
Recommended surrender terms for when our planet is invaded.
Word for when a writer uses alternative spelling.
Those sentences don't sound right, they get the meaning across but are awful! I can think of different ways of phrasing a sentence without using "for when". I view "for when" in the same way I view "ain't no", as in "ain't no world big enough for you". Sounds like a ugly verbal shorthand.
There are instances where using "for when" makes sense, as in:
What to signs to look for when getting pulled over.
But the former sentences don't fall into this category, at least to me. Can someone help me understand if this is a correct way of writing?