The original Francis Scott Key bridge took 5 years to build.
Estimates have been between months to 4 years for a replacement. The primary factor will be what shape the supports are still in, and if they'd even use them or beef them up. So, a design has to be settled on, and funding. Seems like the Federal Gov't will foot the bill (at least until they file suit with the cargo company), so that should speed things up. US Army Corps of Engineers has been activated. So, we shall see...
I'd set the over under at 2 years.