How long should Linux board bring-up take ?
My last project required becoming familiar with a new processor, supporting an entirely new board, and writing 2 new serial drivers. It required almost 3 months, almost 1/2 that time involved hardware problems with the board and approximately 1/3 was required by the new serial drivers

How difficult is it to port a major project to Linux ?
For a project with an impossibly tight deadline I ported a 700,000 line C/C++ system, involving an embedded in memory real-time SQL server, several hardware and protocol drivers for military data-links, as well as a client Software development kit, from Windows to Linux in slightly over 2 months. The was a maximum effort and required nearly 1000 hours. I was also familiar with the code before starting, and was aware of exactly the extent of the windows specific aspects that would have to be addresses. The end result was not a Linux port, but a true cross platform implementation that could be built for either OS, as well as improved and maintained.