The descriptions for those properties are identical
" (string | Function ) - the format of the scale’s labels. If set as a function, expects a date object as a parameter."
Hello Tom,
There is no difference between the properties. In the previous versions, there was a date property name, but when the subscales property was removed, the dev team added the format name to make it clearer how the property is used:
https://docs.dhtmlx.com/gantt/migrating.html#:~:text=%3D%20false%3B-,Time%20scale%20settings,-Configuration%20of%20time
The date property remains only for code compatibility reasons so that if you migrate from older versions, it would still work. You can use any property, and it will work the same way.