Annual submission dates for CMALT portfolio submissions are: 1 Feb, 1 June, 1 October.
You can find links to support documentation and example links at: https://www.alt.ac.uk/certified-membership/cmalt-support
Also for those also considering submission of a portfolio for HEA Senior Fellow there is close overlap with a CMALT portfolio.
You can find HEA fellowship information at:
An example of a dual CMALT/HEA-SF portfolio has been kindly shared by Fiona Harvey: