How to plan itienary in Macau?

Yes, they are right. One day is enough for you to visit that city.
From HK, you may reach the local Maritime Ferry Terminal. Then the Fishermane Wharf, the Sands, the Avenida de Almeida Ribeiro, the Macau Tower, the Ama Temple, the Senado Square, the Ruins of St Paul and Grand Lisoba are suggested.
From HK, you can take ferry from Hong Kong Macau Ferry Terminal to reach M.

What bout the Venetian?

You can also go to Venetian after you visit the Grand Lisoba. Or you can drop off the Lisoba and visit the Venetain directly.
From Sintra along the Avenida de Almeida Ribeiro, you can find the buses to reach City of Dream. Upon reaching City of Dream, you can find free shuttles to reach Venetain or walk to reach that place directly.

So just to clarify.. you saying that after we reach the Ferry terminal of Macao.. we should go to the Fishermane Wharf, the sands, Avenida de Almeida Riberio, etc.. and last to the the Venetian?

Will I have enough time left to cover the Venetian after all of that? Are all the above places in close proximity? Are they convenient connected in terms of transport? What if i plab to cover the Venetian first after reaching macao? Will i get free shuttle from the M ferry terminal to go to Venetian?
Do you know when is the last ferry back to HKG?

As I know, the scenic spots are not far from one to another. If I were you, I would travel in the well-known places in this sequence: Fisherman Wharf - Venetian Resort - M Sightseeing Tower - Avenida de Almeida Riberio and Ruins of St. Paul as well as the Senado Square

You can make full ue of the local bus and the free shuttle buses of the hotels or casinos.

As I know, the Venetian provides free shuttle buses from the ferry terminal. You can easily find upon arrival.

The last ferry back to HKIA leaves M around 20:15.

You could hire a scooter for a day or two, it's a wonderful way to see the sights in M! And you have a freedom to go wherever, whenever you want!

Oh ..how much does it cost? Is it easily available?