frame_time
The option documentation is properly formatted yet
Summary: Frame time (ms) Default: 0 Example: 10 Since: 2.9.7
Specify how long FS-UAE is allowed to emulate and render a frame. This can be used to force FS-UAE to pause after v-sync, before it starts emulating a new frame.
If you are running in PAL emulation, you can for example specify 13 to make FS-UAE wait 7 ms after a frame is done, before it starts emulating the next one.
This option is not tested in all circumstances, and will interfere with fastest-possible modes, etc. The option is not supported in net play mode.
Source: https://github.com/FrodeSolheim/fs-uae/blob/master/docs/options/frame_time