I’m on the 10 year Family route visa and can now switch to the 5 year route. Does time already spent on the 10 year route count towards the 5 year visa?

Only time spent on the 5 year route counts towards the 5 year ILR pathway. If you have spent 4 years on the 10 year route and switch to the 5 year route you still have to complete 5 years on the 5 year spouse visa route.