The best time to visit Sky-deck is to arrive just before sun set as you can witness the both day and night view of the city and surroundings which is stunning.
Apart from viewing through the large glass windows, there is an option to spot the iconic landmarks such as the MCG (Melbourne Cricket Ground), Bolte Bridge, Carlton garden, Art centre tower and many more through the iron fence from one corner (there is a limitation on the number of people at that spot, so at times you can expect a queue near this place). Apart from this, there is another activity called as the "edge experience". By paying additional fees, you have an option to walk on the glass floor overlooking the ground from 297 meters height.
You can book tickets online from their website.
How to reach here: It is situated in the south bank and You can walk from Flinders street station to reach here.
Entry fees: 18 AUD general admission fees
Time to spend: - 1-2 hours
Tip: sometimes the hotels where you are staying have some free pamphlets near the reception area which have some discount on Skydeck tickets or check the groupon website for Melbourne if any discount can be availed.