Hi Conradcp, most kitchen fans are not timer models, so you may need to shop around to find one! Kitchen fans also tend to be 150mm in diamater or larger, whereas standard bathroom timer fans are only 100mm so the hole through the wall will have to be made larger.

Depending on what make and model of fan you have alreay, it maybe that its just a basic axial fan and you could well find that buy buying a decent UK made centrifugal type bathroom fan (e.g. xpelair or vent axia) that it would be just as good as a kitchen fan. You can expect to pay £100 plus for a decent brand of bathroom fan, so the ones you see in wickes etc for £15 are just chinese junk and totatlly ineffective.

If you do decide on a kitchen model and can't locate one with an over-run timer facility, then its worth considering one with a humidistat. This is like a thermostat but will switch the fan on and off based on the relaative humidity level in the room.

Hope this helps, please click on like if it does.