When you perform an operation such as addition, subtraction, multiplication or division on a time expression, the result will depend on the operation. Any operation that involves a time expression and a number would return a result in the form of a number.
Here are the comparisons between 2 operations:
Time + Time
?02:03:04? + ?01:02:03?
Time + Number
?02:03:04? + 65
As it shows, the first operation returns the result in the form of time expression while the second operation returns the result in the form of a number. If you want to obtain a time expression from the second operation, you must use the command Time string. The command Time string returns the string form of the time expression you pass in seconds.
Time String(?02:03:04? + 65) returns 02:04:09
Time String(7449) returns 02:04:09
Reference: Time Operators