> is a numerical comparison operator, and according to JLS Sec 15.20.1:
The type of each of the operands of a numerical comparison operator must be a type that is convertible (§5.1.8) to a primitive numeric type, or a compile-time error occurs.
Your Time type cannot be converted to a primitive numeric type, because it’s not a primitive nor a primitive wrapper. Hence the error.
If you want to compare them, the Time time must implement Comparable<Time>, then you can write:
if (time1.compareTo(time2) > 0) { // Like "time1 > time2"
}