Hi J.
I don't think there are proper ways to do things. There may be traditional ways to do things, but we all know that we can break from tradition and sometimes that is a good thing. With 5:45 baptism, in my humble opinion, you would have to be careful that people did not assume that there would be a meal, supper /dinner, hence the reason you said lite lunch.
If it was me, and it isn't I would say cake following which according to my catering background indicates you best have had your supper. If you have tea sandwiches before, again in my opinion, local people would be so hungry they would eat more than usually expected by the caterer and therefore it looks like the caterer didn't have enough food. Not the case, if you serve little tea sandwiches at 4:30 and people have eaten at noon, they begin eating and usually average around a sandwich. If you serve that same crowd at 2:30-3 PM or say snacks the caterer plans on 1/2 sandwich per person. They don't mean to it is just common. You can serve those same sandwiches with cake after and get away again with 1/2 sandwich or less.
If your crowd is traveling a distance of 2-3 hours or more to get there you really must take that time into consideration. Leaving right after lunch they might not have time to stop for supper before the event.
Now that I may have confused you I will just say, if you are having the affair catered tell them whether it is a meal, and if you are doing it, remember some may regard it as a meal. Going to the church hall, having something put on by the women of the church is a great way to have donations going back into God's work. Just some thoughts to ponder.
God bless you and give you wisdom
K. SAHM married 39 year --- adult children 38,33,and twins 19.