We would like to have a relatively late civil ceremony and would prefer not to invite everybody for the day and wedding breakfast. But, we are concerned that the wedding breakfast will run too late for guests to feel welcome for the evening reception.
In the UK you can get married up to 6pm. As register office ceremonies are a lot shorter than church ceremonies, you should be able to have your wedding at around 4 or 5pm followed by the wedding breakfast at 5 or 6pm. Your evening guests could be invited from 7.30/8.30pm and you could serve a late supper - about 9 or 10pm consisting perhaps of a cheese platter with assorted breads and biscuits, fresh fruit and wedding cake. Or, you could leave a running buffet open throughout the evening so that people just help themselves when they feel like it.
Most people attending an evening reception at 8.30pm would have eaten something beforehand and your day guests will probably be fairly full from the wedding breakfast.
As long as you invite evening guests by 8.30, I think that is fine. If you invite people any later than that, you're expecting them to come to a very short party!
Try not to rush the wedding breakfast to ensure that it's over for the evening celebration.