This cobbler is "done" and ready to come out of the oven when the berry filling is bubbling all around the sides of the baking dish. How long this takes depends on the size and temperature of the berries. Frozen berries will, of course, take longer to bake. Likewise, larger, more sturdy berries like strawberries will take longer than small, delicate berries. How juicy the berries are can also affect the bake time. So, check on your cobbler after it's been in the oven for 55 minutes, then every 5 minutes after that, until the berry filling is bubbling around the edges of the pan.