You can speed up the conversion if you write the source files with a Windows editor. In this case UDO doesn't have to convert the characters from the IBM PC character set into the Windows ANSI character set.
If you write source file with a Windows Editor you have to insert the switch !code_iso inside the preamble of your source file. If you forget to do this UDO will think that the source file was written with the IBM PC character set.
Tip: I recommend to use the "Programmer's File Editor" (PFE) written by Alan Phillips, a really great freeware editor that is available both for Windows 3.11 and Windows95/NT.
Using the switch !win_medium_compression or !win_high_compression you can tell the Microsoft Helpcompiler to compress the final Windows Help file up to 50%. The Microsoft Helpcompiler will need a little bit more time to convert the RTF source file if you use the upper switches.