How are days determined with "in time frame" and "in past" filter constraints?

This is a bit of an odd question, but one I realized I have no idea on: when you use a filter such as In Time Frame: Today or In Past: 2 Days, how is the "day" itself calculated? That is to say, how is a day determined for a given datetime? Is the calculation done by the Location set in Marketo? Is this done at the server level? Is "day" just a human-friendly shorthand for the most recent 24-hour period?

For example, if I have "today" as a time frame filter, does this mean if something is stamped at 11:59 PM and isn't able to be looked at for triggering a Smart Campaign until 12:00 AM, will that Today filter exclude it?