What would be the shortest way one could get to Culross from Stirling if we don't have a car? It looks like a fairly short drive but the trip via train trip extends that and we have time constraints. Is an Uber-type service available in Stirling or do you know of bus service that would get there in a timely fashion?
It looks like Uber is there; see http://uber-rates-stirling-uk.uber-fare-estimator.com/.
Google finds a late bus departure with only one connection like this:
8:33 PM Bus Station (Stance 9) (Platform 9)
Bus 63B towards Tillicoultry
8:56 PM Shillinghill (Stance 2)
9:45 PM Shillinghill (Stance 1) (Platform 1)
Bus 28 towards Dunfermline
10:12 PM The Palace (Culross, United Kingdom)
However, looking at mornings at https://www.stagecoachbus.com/about/east-scotland and https://www.firstgroup.com/south-east-and-central-scotland, I only get results with at least two connections. You'd have to play with those to see if you can get better results or see schedules by bus number.
The National Trust web site only mentions the number 78 bus from Dunfermline.