The day that I consider a "day" is the day that is used to calculate our calendars. The one that requires a leap day every 4 years to keep things on the beam.
Now if you want to have a really interesting discussion...how long was a "day" back in the Book of Genesis?
I have to go to bed. So feel free to discuss among yourselves.
The calendar with a leap year every four years is the Julian calendar and is only used in the Eastern Orthodox Church. We use the Gregorian calendar and have since 1753.