DATE FORMAT

DATE FORMAT

Please advise. Trying to create a spreadsheet where one column contains date in dd/MM/yy format and another contains the time in HH:MM format. My first problem is that when I enter any date, other than one in the current month, the format changes to mm/dd/yy or MMM dd,yy.
I suspect it's something to do with the MM rather than mm? Why is the mm option not available anyway?
Also want to sort sheet on date first and then time so rows are displayed in date and time order. The sort option only appears to work on one column? Do I have to write a VBA module for this?
Want to use Zoho, rather than Google Docs, because of the Macro facility which is not available on Google Docs, but these basic issues will prevent me from doing so unless there is a solution. Help please.