Option B seems better overall, but it would be much more useful if it also grouped photos by exact date rather than just by month.

Option A preferred, this would be more efficient to deal with a large amount of photos. An additional idea: is there a better style than stacking? Maybe choose a few (e.g. 4) representative photos that are drastically different in time or location etc. so one won't accidentally miss the photo in interest because they are at the bottom of the stack.

I really love both!

Both would be fine. I think A would be the one I would like to see you start with. Perhaps a date scale on the side to quickly move through the dates. Could it be zoom-able? Zooming in from year to month and then week/day. Holding down a keyboard key while zooming with the mouse wheel. Sorry, no drawing talent here.

I think both options eventually would be great, but if I could just have one I'd go option A

I'd prefer Option B

option B preferred