So, the estimated times listed on a Google Map are based on algorithm that is supposed to take into account current driving conditions. So, if you ran the same route, on Google, once a day for a week or so, it would--most likely--give you different times. As a reality test, having driven to Yosemite from Las Vegas a bunch of times, the average speed that you can expect to achieve is 57 mph and that is assuming that you can drive 80 mph in certain stretches. If the weather is not cooperating or there is Tule Fog in the valley -- which is possible--that trip could be much longer than eight hours.
The other reality is that Google Maps do not take in account, stopping for fuel or food or construction delays.
Mark