One point to consider....Concrete takes a curing process that requires pre-stressed concrete to cure over a 28 day period before heavy loads can be driven across it. (Unless the Russians have discovered some magic process that does not require that).
Depending upon the building process being used...that could mean a sequential replacement of spans that add to the period of time to complete the whole structure.
The Bridge crew around the corner building our new bridge completes one section....allows two weeks for a partial curing....before driving light vehicles onto the new section....and are working on the next section while the first cures.
They are using a combination of barges and a temporary bridge to build the permanent 3200 foot long bridge.
Working two Shifts a day we can see progress being made...but we are talking years before the project is done.