They won't build a whole new maching they will simple replace your with a brand new one and send it back to you or they will replace the GPU like they have done with mine.
Mine has taken 3 weeks so far this coming Tuesday will be the forth week but they phoned me on Thursday to tell me they had the part and had arrived and they were going to install it and test it then they would send it out on Friday.
Alas it either took longer to test or something else happend as it didn't arrive on Friday.
Any way Good luck with having a smooth RMA process.