Did you look into Parse & Format Date Function Calls? e.g. to get current date you can use formatDate([%CurrentDateTime%]).
Hope this helps!
Use the various values at your disposal: [%BeginOfCurrentDay%] has the time set to midnight. There are others as well, most easily found in the microflow expression editor, when creating/changing variables or setting a value on an object. The TrimTo… functions help you to trim any date/time value to the desired value.