This isn't possible.
However, there are some ways around this. Depending on my schedule in the morning, I need to wake at either 3AM, 4AM, 5AM, or 6AM. I want the same wakeup flow (slowly turn on bedside lights, turn on water heater, etc. etc.).
So I use a single flow with four WHENs (Date & Time), each of which is modified by an ONLY IF (Functions:Variable). I use Alexa to set the value of the Functions:Variable. Once that's done, then my wakeup flow runs at the desired time. Every morning at 8AM, I have another flow set the Functions:Variable value to be such that my default wakeup time is 5AM.
My Alexa commands are "Alexa, turn on wake me up at three", or "Alexa, turn on wake me up at four" etc. These commands simply set the Functions:Variable to be 3, 4, 5, or 6. When the flow runs, the WHENs trigger only if the corresponding ONLY IF has the correct value. So, if I have set the ONLY IF to be 6, then at 3AM, 4AM and 5AM, the WHENs don't trigger because the ONLY IF doesn't match 3, 4 or 5. At 6AM, the WHEN triggers the flow because the ONLY IF matches 6.
In your case, your flow would have 24 WHENs and 24 ONLY IFs. I would recommend using military time (so 0 to 23).