can i stain a light timber veneer a darker colour?  I want to keep the
timber look
but darker,

Yes you can stain a light timber veneer a darker colour. You can stain
most veneers as long as the veneer is a wood. To pick the darker
colour, a good way is to buy some sample bottles (such as Minwax or
others) and apply a small dab on the veneer in an out of the way spot.
Probably a good paint or stain company could advise you what darker
stain to buy to get the look that you want.