To replace the functionality of the MessageBox with a LogMessage during mock testing, the developer can perform the action of Surround activity with mock. This action inserts a mock activity around the selected activity, which allows the developer to change the behavior of the activity for testing purposes. For example, the developer can right-click on the MessageBox activity and select Surround activity with mock from the dropdown menu. This will create a mock activity that contains the MessageBox activity. The developer can then edit the mock activity and replace the MessageBox activity with a LogMessage activity, which will write the message to the output panel instead of displaying it in a dialog box. This way, the developer can test the functionality of the workflow without having to interact with the MessageBox dialog box. References: [Mock Testing], [Surround Activity with Mock]

In UiPath Studio, you can use DateTime and TimeSpan variables to store and manipulate date and time values.
A DateTime variable represents a specific point in time, such as the current date and time, or a date in the past or future. A TimeSpan variable represents a time interval, such as one hour, two days, or three weeks.
To show what hour was 12 hours prior to the date from the variable, you can use the AddHours method on the DateTime variable and pass a negative value. For example, if you have a DateTime variable called CurrentDate that stores a date and time value, you can write:
CurrentDate.AddHours(-12).Hour
This expression returns an integer value that is the hour component of the DateTime value that is 12 hours before the CurrentDate value. For example, if CurrentDate is 2024-02-08 10:51:49, then the expression returns
22.
The other options are not correct expressions for showing what hour was 12 hours prior to the date from the variable. Option A is invalid, because the DateTime class does not have an AddHours method. Option C is incorrect, because the DateTime variable does not have a SubtractHours method. Option D is incorrect, because the DateTime class does not have a SubtractHours method.
References: Variables - Date and Time Variables - UiPath Documentation Portal, DateTime.AddHours Method (System) - Microsoft Docs, Date and Time Arithmetic - UiPath Community Forum