Hi Mary, for what it's worth

I always router mine after it's fitted. I find it tends to hide the mistakes underneath it better

Just be careful not to use to much pressure holding the router against the TD. Two light passes are much better than one heavy one.
Cheers
Paul
Just remembered(it hurts) Do not hold the router in one spot for any length of time otherwise you will end up with a burn mark. Use a continuos motion along the length. If you need a rest, pull the router away gradually. Then feed it back in from where it is already trimmed.