We traveled in early June where there are snow aplenty up the mountains. Stayed at Te Anau for 2 nights to self drive to Milford. For those whom are deciding to self drive, better to check the Milford Sound road website to know the road conditions, whether snow chains are required. I checked both the road condition site & weather forecast to get a better feel of how it is going to be.
We drove in on a cloudy & sunny day, road was good with sections with warning signs of black ice. It is not as a difficult drive as many had warned. Yes a couple of windy roads with some elevation, so just drive slowly if no confidence. A couple of pitstops along the way to rest yourself.
As many has suggested, leave earlier to avoid traffic.
We were in winter month, so daylight from 9 to 5pm only. We left at 8am from Te Anau & reached Milford cruise center at about 1045am. Did short stops in between.
As weather was cloudy, foggy during the start of the journey, mirror lakes & Elington were not ideal.
I booked the cruise ship from Bookme, cheaper deals if u able to grab the right time. $50 pax for cruise on Mitre Cruise, smaller ship which can get closer to some of the falls.
The bigger ones have meals servings on board but have to pay extra.
My advice is if u like to save money, pack some sandwiches/meal & drinks to eat on board the cruise.
The hilite of the journey is near to Homers tunnel, where you will be surrounded by majestic snow capped mountains.
Thus self drive is possible with bit of luck and confidence. But go ahead to pay for coaches if u like to just sit back & enjoy the trip/view w/o worries.