Save the date/evening Cards

I wouldn't send save the evening personally and def don't send save the date to evening only people - they might think they are coming all day !

Personally if I was only invited to the evening of a wedding it wouldn't stop me booking a holiday or weekend away or going to another all day wedding etc. And as you will prob send the invites out 2 or 3 months before people won't have made arrangements for just a night out that long before the date. So people won't cancel or not make big plans but will not have made smaller ones by the time you ask them ! hope that makes sense !

We can only have a small number in the day but are inviting all the night people to the church as well and for photos at the church after so they are only really missing 2-3 hours of the formal meal

I would just make sure people know when the date is, it shouldn't be too hard I know everyone kept asking me if the date was set. Depending on when the wedding is you could maybe put a message in christmas cards mentioning they will be invited to the evening do on such a date.