Traditional and Roth IRA contributions are linked to the tax calendar.
The 2021 IRA contributions can be made anytime from January 1st 2021 until the day tax returns are due in April 2022.
The 2022 IRA contributions can be done anytime from January 1st 2022 until the day tax returns are due in April 2023.
During the period between January 1st each year and ...
I get around to doing it in December, can I make the maximum contribution all at once in that month
IOW make your max 2021 contribution.
and then also make the maximum contribution for the next year in January?
Meaning you make your max 2022 contribution.
Thus... yes, you can make a contribution each calendar year for that specific year.