I've attempted this monster day hike three times, twice without snow, but first time was with snow in late May during a year with slightly less snow than this year. Without snow you need every minute of daylight in June to pull it off and go from the Bridalveil Falls parking lot over to Glacier Point and back down. On those long June days I started at 5:30 am in the morning and barely got down to the Valley Floor again by sunset at 9 pm, and then I had to walk by flashlight a few miles back to the car. You will be lucky if your feet are not blistered somewhere at the end of the day and your knees are still working well.
The first time I tried this hike was in the snow. We lost the trail in the snow after the first lookout point above the old road, and we tried our best to make our own trail and follow the license plates used by the skiers when we could find them. We started around 8:30 am at the Wawona Tunnel, but starting 3 hours earlier would not have made a big difference unless we had turned around sooner. We got close to Bridalveil Creek before turning back, since we had no chance of getting to Glacier Point before dark with 3 hours left of daylight. On way back we ended up higher than the trail to avoid getting too close to the edge, and overshot the area where the trail descends down to the tunnel entrance. My GPS unit died in the middle of this, so we were on compass most of the time and didn't get out before it got dark. We slept over 1000 feet above the middle of the Wawona Tunnel, against a rock that was sticking out of the snow. It was probably the most scenic campsite I've ever had, as I could watch multiple waterfalls, domes, and car traffic on multiple roads from our high vantage point. Since it was a warm day/night for May with no wind, my friend and I were able to avoid hypothermia by sleeping next to each other and putting our bare feet in our daypacks (since all of our socks were wet). It was easy to get out the next morning, as we skiiied downhill in our boots to the old road and then followed it back to the trail.
The bottom line is that even if you have transportation waiting for you at Glacier Point, odds are not good that you will get through all the snow between the Wawona Tunnel and Glacier Point during daylight, and this is not a good area to wander around in at night, since you are very close to a steep dropoff much of the time. Right now there is a part of the 4 Mile Trail that is closed due to dangerous ice conditions that make it easy to fall a long distance. Usually it opens up by the time the road to Glacier Point opens, but this year could be different. If you start early in the morning from the Glacier Point Road where it crosses over Bridalveil Creek, you should be able to reach either Glacier Point or the Wawona Tunnel, depending on which way you go when the trail forks (at the next bridge over the creek), before daylight is gone. That's the only way I would recommend going when most of that area is covered in snow. Not only does the route finding and sinking into snow slow you down by a good 50%, but there are numerous seasonal creeks and snow bridges to deal with. Following other hiker's tracks is a bit risky, since it is easy to get lost in the forest and not take a direct path once you are away from the edge, which happens for a few miles on both sides of Bridalveil Creek.