I need a formula that has a cell which counts dwelling time in hours between: Cell A2 [=NOW() function] and [mmm dd yyyy H:mm) date format] 
Example:
How long a package has been on a front door step,
in A1 [this is the date and time the package arrived], A2 [Is the =NOW() function]
I want A3 to display difference in time in hours between A2 and A1,

Example:
How long a package has been on a front door step,
in A1 [this is the date and time the package arrived], A2 [Is the =NOW() function]
I want A3 to display difference in time in hours between A2 and A1,
