Ah. The simplest and most performant way to identify if two date objects share the same “date part” (as you might call it) is textwise (this is a special case of date comparisons and not generally true of date evaluations – most should be performed datewise):
date1:formatted as MM/DD/YYYY (some_timezone) is date2:formatted as MM/DD/YYYY (some_timezone)
… will be true if date1 and date2 happened on the same date. The :formatted as parameters following date1 and date2 must be identical for this to work properly. It does not matter which timezone you select, just that they be the same. So you can use User’s Timezone or a static timezone of your choice.
Example:
date1 is January 28th 2019 at Noon in America/Los Angeles
date2 is January 28th 2019 at 1:22 PM in America/New York (aka January 28th 2019 at 4:22 PM in America/Los Angeles)
Let us say that Current User’s browser believes it is in America/Los Angeles.
date1:formatted as MM-DD-YYYY in Current User's Timezone
… resolves to a string: “01-28-2019”
date2:formatted as MM-DD-YYYY in Current User's Timezone
… resolves to a string: “01-28-2019”
These strings are the same, so
date1:formatted as MM-DD-YYYY in Current User's Timezone is date2:formatted as MM-DD-YYYY in Current User's Timezone
… resolves to the Boolean (“yes/no”) value yes/true. Indicating that these date/times happened on what we think of as “the same day”.