It's the same as you can use in Eikon Excel. You can view the explanation in Eikon Excel Formula Builder or in Data Item Browser app in Eikon by clicking on the question mark icon next to a date field in the Parameters tab. Here's the screenshot.
I have specific request in the ek.get.timeseries() function. I would like to see if its possible to expand this field to see 2 hours,3 hours,4 hours,etc data bars instead of just tick,second,minute,hour ..