It's a 3pm church wedding, formal but not super formal. the dress is a red jersey day dress but long (maxi) with a twist / knot front. I've worn it to a wedding before but that was in another country and was a different type of wedding with more laid back people.
I would wear it with nice heels, fascinator thingy and a little clutch bag.
I have got an alternative dress, shorter phase eight silky patterned jersey but it's less comfortable and I'm already feeling miserable with pmt bloat and sore boobs.
I think the rule is that if it starts before 6pm, I'd wear a shorter dress (knee or calf length), and if at 6 pm or after, long is better. However, this year maxis are everywhere, so you can get away with a long dress. Cover your shoulders in church though.
I just attended a smartish 3pm wedding a week ago and the majority of guests wore short dresses but I could spot a maxi or two.