Source: The False Bride
Claire gets lost in the woods looking for Clarence during a lightning storm. She takes shelter beneath a fallen tree where she finds a skull and a stone. When she looks up she can see a torch coming through the forest. Assuming it is Jamie she calls out to it but soon notices that as the figure approaches it disappears and reappears.
When it gets closer the figure it that of a native with the gem around his neck. Claire realizes it is a ghost and asks what it wants. The figure turns and leaves.
The next morning, Claire wakes to find her shoes missing. She does; however, find tracks which she follows to a stream where Jamie waits. Jamie follow similar tracks to find Claire's shoes by the stream.
Claire can only assume the ghost brought her shoes there which brought Jamie and Claire back together.
When Claire goes to wash the skull in the creek she discovers he has silver fillings which won't be invented until 100 years later.
This means the man has to be a traveler like Claire.
How many travelers are there? We know of Geillis and Claire and now this man who is called Otter Tooth in the credits.
SOURCE: The Bakra
When we meet Lord John Grey again we realize he wears the sapphire Jamie gave him as "a token of their friendship" which we all knows means that John has it bad for Jamie. Meanwhile, Geillis is looking for the third sapphire which was removed from the treasure box on Selkie Island. She believes that if they all three are brought together with Margaret Campbell's abilities the Brahan Seer's Prophecy will be revealed. Geillis manages to accomplish this goal and we get:
When twice twelve hundred moons have coursed.
'Tween man's attack and woman's curse
And when the issue is cut down
Then will a Scotman wear a crown.
Geillis and Archibald Cameron decide on the meaning of the prophecy: The twice twelve hundred moons refers to 200 years time. The man's attack and woman's curse is the conceiving and birthing of a child. And cutting them down means to kill the child but it would appear it is referring to a 200 year old child.
SOURCE: Freedom and Whisky
Brianna gives Claire a topaz necklace for the passage through the stones. Claire comments that she had on a jeweled watch when she went through the first time and Jamie's father's ring when she went through the second time.
Roger believes this means they protect you.
How then did Geillis steer her time traveling?
SOURCE: Dragonfly In Amber
Claire herself tells us Gillian believed you needed a human sacrifice and gemstones to protect and guide. So does this mean a gemstone is needed to control the distance of your travel which would explain Geillis large jump.
SOURCE: Through A Glass, Darkly
Claire left Jamie in 1746 and returned to Frank in 1947. That is a 202 year difference.
She traveled with Jamie's father's ring and it was missing the stone when she got to 1948.
Geillis/Gillian goes through the stones in 1968 and clearly travels back more than 203 years because she's there before Claire. We don't know if she got there 1 or 5 years before but if she got there 5 minutes before then she went back 225 years. Clearly she was there enough time to establish herself and seduce Arthur Duncan into marriage so I'd guess 230 years.
Is there a default of 202 years?
Are the stones protection?
How do you steer?