Heat the oven to 200 C / 400 F with one rack in the middle and one in the lower third. Toss the grapes with the olive oil, salt, and half of the thyme in a 23 x 33 cm / 9 x 13 inch baking pan.
Line a 33 x 46 cm / 13 x 18 inch sheet pan with parchment and unfold the puff pastry onto it. Use a knife to score a border 2 cm / 3/4 inch from the edge, without cutting through. Prick the center all over with a fork and brush the border with the beaten egg.
Put the pastry on the middle rack and the grapes on the lower rack. Bake the pastry for 10 minutes, until the border is puffed and light golden. Leave the grapes in for 15 minutes total, until most skins have split and the juices bubble.
Press the puffed center of the pastry down gently with the back of a spoon. Stir the ricotta with the lemon zest and pepper, then spread it inside the border. Lift the grapes out with a slotted spoon and scatter them over the ricotta, leaving the juices in the pan so the pastry stays crisp. Crumble the feta on top.
Bake the tart for 15 minutes, until the border is deep golden and the feta edges start to brown. Let it rest on the pan for 5 minutes. Drizzle with the honey and 1 tablespoon of the pan juices, scatter with the remaining thyme, and cut into 6 pieces.