I had a similar problem to contend with a couple of months ago. I too started from Ivybridge, also a bit late in the day and just decided to start hiking. I had the benefit of longer hours of daylight which you won't have. Get off the train and turn right, once you get to the bridge, the left road drops down into Ivybridge, over the bridge to the right is the Two Moors Way. Within a mile, you will be on the moor proper, open land all around you and you will find many places to wild camp as I did. If you keep walking you will eventually come to a grassy hill (Butterdown Hill I think its called) directly in front of you, the track veers off to the left. If you prefer to camp higher up I think this will be your place for the night?
In my case, I kept going until I came to a stone marker (its marked as 'stone marker' on the OS map) which identified the Two Moors Way to the right, its quite a long way onwards, not good enough I would think to make the effort but you have to be the one to decide. Just before this point there is an old ruin and if necessary you could camp and shelter by the low stone walls but you may find a lot of sheep droppings everywhere. At this point, I walked on past for a few hundred yards, found a patch of flat grass and pitched my tent for the night. Windy overhead but I was in the shelter of tall grass. If by chance you do get to the stone (it will be difficult for you to make it in daylight I think) and follow the Two Moors Way route it soon drops down to a stone bridge, cross it and turn left until you come to a gate/stile, jump over a good flat spot there.