Letting people know the date

Not so much silly as pointless, since long before you send the invites out, people will probably have forgotten you've already told them!

The only exception might be people who need to plan well in advance to be able to attend - e.g. if you have any overseas friends and relatives who only visit the UK every 2-3 years, you might want to flag up your wedding date to them so that they can plan their next trip around it! It would be sad if they booked a trip here for next year and then couldn't afford to come back in 2026. But for anyone else, I'd leave it closer to the time. No one is going to keep the same 'save the date' notice on their fridge for two whole years!