A company is required to have a financial year. This means there must be a start and end date.
It's standard practice for companies to have their financial year end on the 28th February each year, so their financial year starts on the 1st March of each year.
This makes things easier as it's also when SARS's requires you to submit tax returns.
A company may change it's financial year end at any time by filing a notice of change to the CIPC.