Re: Asking to Postpone Shodan Test?
Others have said that if your sensei thinks you're ready to test, then you're ready.
When coaching for a competition with relatively new people (in my work, not in Aikido) I ask - "Are you ready? - Say 'Yes,' because the race is in x hours - you've done all the available training time, planned and prepared, so - even if you're not completely ready, you have to be ready..." or something to that effect.
Another interpretation of "you - take the shodan test in November" - is - your sensei now feels you're ready to start understanding what you've been learning to date. Way back in the days of Aikido-L, Rocky Izumi posted a great article about people who refuse to take grading tests - wish I could find it.
pass/fail - no matter - learn from it...