Both Apple and Google Maps greatly underestimate travel times on anything other than perfectly straight motorways. If you've never driven here before you can at least double their estimate, easily - and that assumes you are at least reasonably proficient at driving on the left at all.
The A9 is the most dangerous road in Europe, and you'll be doing 50mph at most along that because there's nowhere to overtake and that's the maximum speed trucks can go at, so you'll end up in a queue behind a truck.
Depending on the route you take, you might go through Inverness, in which case once you get off the A9 most of the road you'll be on looks like this, for about 120 miles: https://maps.app.goo.gl/9L5cSejT1eyAVR2E7
Once you get to Dalwhinnie you can turn off the A9 and start heading across to the A82, which is really pretty especially in the snow but will be mostly road like this: https://maps.app.goo.gl/qv1L21jk59EEAHZs9
Notice how it's not actually wide enough for two cars? But that's still a 60mph road, although you'd be lucky to be getting up to more than about 50mph.
And you'll be driving on the wrong side of the road, in an unfamiliar car, with a manual gearbox.
The A9 is the most dangerous road in Europe, and you'll be doing 50mph at most along that because there's nowhere to overtake and that's the maximum speed trucks can go at, so you'll end up in a queue behind a truck.
Depending on the route you take, you might go through Inverness, in which case once you get off the A9 most of the road you'll be on looks like this, for about 120 miles: https://maps.app.goo.gl/9L5cSejT1eyAVR2E7
Once you get to Dalwhinnie you can turn off the A9 and start heading across to the A82, which is really pretty especially in the snow but will be mostly road like this: https://maps.app.goo.gl/qv1L21jk59EEAHZs9
Notice how it's not actually wide enough for two cars? But that's still a 60mph road, although you'd be lucky to be getting up to more than about 50mph.
And you'll be driving on the wrong side of the road, in an unfamiliar car, with a manual gearbox.
Good luck.