We are doing something similar in reverser order, (Ceremony, picnic, desserts)
I think you timing might work, but my concern would be the getting ready time.
1. If you are not wearing your dresses to the picnic (which I assume you woudln’t) are you/ your bridal party going to have enough time to get ready (hair, dresses, shoes, getting ready pictures) Between the 5:30 and 6:15 time slot? keep in mind it takes longer than you think , and plan at least an extra half an hour becuase you knwo somehting is going to go wrong that will need extra attention.
2. Timing… I think your timing might be a little off for people who are on set eating schedules. (elders, young children, pregnant women, diabetics etc) if you don’t have any of them invited you might not have to worry about it, but 3:30 is a little late for lunch and way early for dinner for some folks, if you have them there until 9:00 are they going to be starving?
3. The concept of food and celebration is… just that… to celebrate what just happened. Now I personally am not one for tradition, and have done a bit of tradition smashing recently so I think if you love this order then go for it and I as a guest would just bring my own sandwitch for after the ceremony, but it seems strange to eat, drink, and be merry with your guests if you have not done anything to celebrate yet… i.e. get married.
Whenever-3:30 Punch and snacks for guests at church, desserts, or maybe just lawn games to keep them occupied, party gets ready,
3:45-4:45 Ceremony and all that jazz as fancy as you want to make it
5:00-6:00 mass migration to park, bridal party pictures, people start the grills and get the picnic ready, you and party arrive to a meal waiting for you and happy guests playing lawn games while they wait
6:15 Eating, laughing, dancing (only if you want to) and all the rest of the ‘celebration’ things that go with after weddings