Found your enquiry on an idle search - I am not involved in researching the name as yet, but the following may help.
My wifes family is Timbrell, we currently live in Llanelli in West Wales. Her grandfather Thomas Timbrell originated from Porth in the Rhondda Valley.
Not too many Timbrells in Wales - I believe the name may originate from South Gloucestershire - large number of Timbrells residing in Dursley. A migration from this rural county into the booming industrial areas of South Wales in the 19th C may account for presence of Welsh Timbrells but I'm just speculating here.
What's your connection.