Q: Propose a new/alternate time to a meeting invitation in Calendar

Hi Guys,

I received a meeting invitation for next Monday at 10am which I accepted. However now I'd like to propose we meet at 9:00am instead. When I go into Calendar on my Mac, I can open the meeting, but the beginning and end times are shaded out. Theres no button to propose a new time. The only option I have is to change my status from Accepted to Declined or Maybe. How do I maintain my acceptance but propose a new time? Also, how would i do this upon first receiving the invitation (prior to accepting). Thanks.