Cashy it usually gives timings per pound and oven temperatures on the wrapping...or somewhere on the packaging.
I have a gas cooker so can only give gas temperatures.......I would say 25mins per pound at gas mark 5.......and an extra 25 mins on top.......check the turkey crown regularly......it can be considered cooked when the juices run clear.
Allow the cooked crown to 'rest' for 30 mins before carving(I would cover the cooked crown with tinfoil to keep the heat in...and in my house to deter the cats from stealing it
)....while the crown is 'resting' make your gravy from the juices.
There Cashy! is that better?