Kelpie-i,
IF you are going to have it operated on do it now. Just because it is classified as benign does not mean that it doesn't eventually grow into the adjacent areas of the mouth. Benign just means it doesn't spread to other parts of the body.
If you wait until it is "really" causing a problem, it may be too complicated to fix. Better to get it now when it is small OR decide not to operate at all.
This sort of tumour is centred around the root of one tooth in the mouth which means removal of the tumour is usually removal of teeth (plural) and part of the gum (but the bigger it is the more they have to take).
My miniature schnauzer (gone to the bridge last year) had one removed at the age of 9 years in 2004. He lost a number of teeth but recovered well. There was no re-occurrence. His tumour was fast growing so the choice of surgery for us was a no-brainer.
The following is a link to the most extreme case I know about http://www.pugrescuenc.org/pumpkin.htm