I have a long sequence (canon dslr and titles) (1hour) and as a test export 1 minute at h264 Blu-ray pre-defined setting (pal 1920x1080, upper field, low quality). This takes approx 1 minute to export. I then export the entire sequence but rather than the expected 60mins to export it takes 3 hrs. I'm running a i7,6Gig ddr3 ram, NVIDIA GeForce GTX 470, windows 7 64bit. Exporting directly from premiere cc. I've also noticed sometimes the hard drive gets thrashed when opening another program, could this be memory / page faults occurring ? The question is why is export time not linear? and how can I improve export time?
I doubt it is memory or page fault related. Encoding is more of a stream operation, you load a frame, process the frame, hold the frame until you finish a group of pictures and then encode the group of pictures. It is not a memory intensive process unless you are doing fancy effects that require memory to process. It is a potentially HDD stream intensive process as it has to stream the video sources off the HDD and then record the output back to the HDD, which could involve lots of seeks potentially to move between reading and writing.
The two things I would try would be to try CUDA acceleration first and see if you can offload the processing to your GPU. If that doesn't get sufficient speed I would try making sure your system is defraged and if that doesn't give sufficient speed, I might try SSDs for processing to and from for better random access of assets.
It is also possible that it is simply harder to encode later parts of your video though. Depending on the exact settings you are using, changes in the content of the video can make a significant impact on how difficult it is to encode the video, so it may not even be unexpected that the encoding time changes between the first minute and the rest of the video.