No, there is no way get a time estimate.
Some suggestions:
- Buy more memory. If subroutinization is taking hours with a Roman font, it may be becuase it is taking so much memory that the workspace is getting mapped to virtual memory on disk. This will slow subroutinizarion by up to a factor of 100. Next time you subroutinze the font, watch the memory usage to see how much you need. Most of CJK fonts need less than 512 Mbytes, and only one goes up to 800 Mbytes while subroutinizing.
- Save the subroutinized CFF table as a file by using the OTFTableEditor. You can then cycle through mutliple builds while testing feature file changes, with subroutinization turned off. When all done, use OTFTableEditor to copy the subroutinzed CFF table back into the font. This is what we do with our CJK fonts, when fixing feature file problems. Of course, this only works if you are not making changes to the source Type1/CID font .