Hi Mmmbop,
I recently applied for citizenship and one of the questions asks if you intend to travel in the next 12 months - if you answer yes, you have to give an approximate timeframe and details of your trip. If you're out of the country when the department comes to consider your application, I don't believe you can progress any further.
From the Citizenship eligibility page:
Location at time of application approval
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If you apply for Australian citizenship on the basis of meeting the requirements for:
general eligibility
having a permanent or enduring physical or mental incapacity, or
being a person aged 60 or over or having a hearing, speech or sight impairment
we must not approve your citizenship application if you are outside Australia at the time we decide your application, unless:
you satisfied one of the special residence requirements, or
the spouse or interdependent partner discretion was applied to assist you to meet the general residence requirement