I need to wake up my mac with my power button

G'day Quentin0451,

Thanks for posting your question about your Mac and sleep mode. I'm glad to see if I can help.

To confirm, you're only able to wake your Mac with a press of the power button. Is that right?

Does the issue only occur after 6-8 hours as you mentioned, or are you able to replicate the issue after shorter sleep times as well?

Under System Preferences > Energy Saver, is "Put hard disks to sleep when possible" checked or unchecked?

Depending on the answers to the above, you might find of the information in the "If your Mac doesn't wake when you expect" section of this link to be helpful. The text below in particular may account for what's happening: If your Mac doesn't sleep or wake when expected

"Your Mac might pause a few seconds before it wakes up. If it doesn't seem to wake at all, check for these possibilities:

• Your screen brightness might be turned down.
• If you're using an external display, your display might be turned off. 
• Your Mac might be in safe sleep. To wake from safe sleep, press the power button.
• Check for a sleep indicator light, if applicable, and make sure that your Mac isn't turned off."

I hope this helps. Best wishes.