If when = "at what time", then you can't say "Let me know when works for you" because you can't say "Let me know at what time works for you". By saying "when wo

If when = "at what time", then you can't say "Let me know when works for you" because you can't say "Let me know at what time works for you". By saying "when works for you", you're trying to use "when" as a noun phrase. But "when" is not a noun, "time" is. Would you also use "how" in this way? "Let me know how works for you" instead of "Let me know what way works for you"?