You cannot hit any target unless you maintain a constant airspeed and altitude.
If that's true then no-one would ever be able to land...
The 'keep the dot on the target' method will always work. As others have said, it may not be the most efficient interception method but you'll get there in the end (even if the target speed vector is changing)
as long as the intercepting aircraft has the performance and manoeuvrability to keep the dot there.
