Running Linux Mint 17.1, 64 bit
AMD Phenom II 550 (yes, a bit of a dog), 8GB memory

Running two models ('cos there are two cores), time predicted for each was 158 hrs
Time so far for one is 160 hrs, remaining 39...
For the other is 193 and 43...

Time remaining goes something like this:
43:17:40
43:17:39
43:17:38
43:17:37
43:17:40
43:17:39
43:17:38
43:17:37
43:17:36
43:17:40
43:17:39
43:17:38
43:17:41
43:17:40
43:17:39
43:17:42
43:17:41
43:17:40

and so on - increasing.

Should I expect this to reverse at some point, or is this a lost cause?

it's now peaking 43:17:56...

It is pretty standard for the time estimates to be out for the first few tasks. Estimates should get better once a few have been completed. At least with Linux we only have the one type of task at the moment as running multiple types of task can mess up the estimates for the others a bit. If memory serves correctly, (my own not the computers) I think estimates were pretty spot on once I had completed 8 or ten tasks of a particular type with no others to interfere.

The total runtime for those on your PC should be about 300-325 hrs. As Dave said, the first time you run some of these tasks, the estimates may be way off. Continue on...