Simple answer No. The new timers do not require a neutral connection if fitted this may need tapping up or other wise made safe. Also new switches tend to have extra functions like change over contacts rather than off and on but careful noting and reading and a basic electrical knowledge and you should be OK. Some are 24 volt most 230 but the new ones are normally volt free so does not matter. Tend to be smaller so you may need something like a blanking plate to hide hole. I fitted a Horstmann DRT2 to mine and it has worked very well. The wiring diagram although small shows plainly how the NO and COM has the wires and NC is unused.