Perhaps, however the time that it takes to sweep one way and then to return can be factored in. The efficiency may be at 80% or so, depending on the extra delay that you add, but seeing as how simple and pretty consistent it is, that shouldn't be a problem for a build this size.
The problem is that wheat grows in random ticks, so you would lose a lot of efficiency from this system (plus I personally don't like using timers because they used to (don't know if they still do) cause lag and crashes)