Can a day in the Gregorian calendar correspond to two different days in the Islamic Hijri Calendar?

I am developing an application which allows users to convert from Gregorian to Hijri dates and vice-versa. I am thinking about whether to just have an input box for the date (e.g. 8/21/2021), or to have an additional input box for the time (e.g. 6:00 AM), as I have heard from others that a new day in the Hijri calendar can start in the same day in the Gregorian calendar? Furthermore, does the Islamic Hijri calendar run on a standard 24-hour day just like the Gregorian calendar?