16 bit program

[an0rma1]

post a link if you like, I really still love to reverse dos stuff
for DOS you could use many tools, native debuggers, as TR (with a very good and scriptable VM debugger), TRW, TurboDebugger, CUP386 unpacker (with vm debugger), etc...
Modern debuggers and Dosbox's, or even use Ida to disassemble and comment, and Dosbox debugger in another window (as I like to do, specially when reversing, not just bytepatching)

You could probably patch timer interrupt, or check if the program is keeping a internal timer driven by this interrupt.

I've uploaded here sometimes a collection of dos cracking related tools I keep upgrading (and been done for years) Also been trying to do a MsDOS scene releases pack, but many files seem lost for ever...