I agree that the words are clear and simple. They refer to a day with a morning and evening, which specifies which of several possible meanings of "yom" (day in Hebrew) was intended.They are clear and simple.
I find it odd that a smart fella like you is having such a hard time with it.
I find it odd that you would interpret them to mean an inexact but protracted period of time,then go ahead and call the words clear and simple.
It's apparent to others what you are doing even if it is not to you. It's done millions of times a day every day, and has resulted in tens of thousands of Christian divisions, each with thousands of individual that can't agree among themselves what their bible says, but each claiming that it his version is clearly and simply correct. The Christian bible says nothing if it can be used to say whatever you prefer.