It depends on when in the year you are. Ignoring precessional issues, which will not be vastly relevant over one year...

It will be twice the number of days until the next solstice (either one) before the sun rises in the same position again. If it's a solstice, it's a year.

Example. It's a week before the solstice. The sun will rise in the same spot in 15 days ( week x 2 plus the solstice)

This is assuming the boulder isn't on a glacier moving down the valley, or anything else