When comparing date/time values, it is better to use the date/time comparison functions.
You can use the IS_BEFORE, IS_AFTER, and IS_SAME functions, or you can use the DATETIME_DIFF function.
TODAY() and NOW() are not continuously updated. You may need to reload a base or view in order to update them.
TODAY() and NOW() return the GMT date and time, not local time. So if your {Check-in} and {Check-out} times are displayed as local dates, your results might be off by a day.
@Pjero_Kusijanovic Oh okay, you didn’t mention that it was a Lookup field… key piece of information there! Glad that you got it working with the other Date functions that are available to you.