Mr Shanahan said after the lifting chains had been set in place cutting on the block would begin on the second section, which would take about 18 hours to complete.
Once this section was ready to be lifted the RMG 1000, along with the first accommodation block, would go back out to sea to retrieve it.
The cut and lift operation to remove the first 350 tonne metal block ended up taking 12 days to complete, after an initial estimate of four days.
Mr Shanahan said during the first lift attempt last week - the lifting chains tore through the starboard section.
"It was never going to be easy, in salvage anything can happen, there is a really high degree of problem solving, for example the fact that weather conditions deteriorated on site and we had to bring it in behind Motiti to finish it off just highlights the reality of trying to conduct an operation on Astrolabe Reef."
Mr Shanahan said they hoped they would be able to lift the second piece of the accommodation block straight off the Astrolabe Reef.
"It would be quite difficult to say if the second move would take 12 days again or just four.
"In theory you can do it in up to four days, but you have to have everything go your way with no margin for error during the operation, one little thing can cause significant delays."
Mr Shanahan said he did not know the proper break down of the accommodation block cost, but it would be "definitely in the millions per month."
The Rena ran aground on Astrolabe Reef on October 5, 2011, while sailing, in clear weather, from Napier to Tauranga. It had been suggested removing the entire wreck could take a decade.