Incident management (as any other ITIL process) implementation duration depends on many parameters which are case i.e. company specific:
- existing process - use this free ITIL Gap Analysis tool to check how your process complies with ITIL recommendations https://advisera.com/20000academy/itil-iso-20000-tools/itil-gap-analysis-tool/
- know-how - knowledge level of our staff influences pace of the implementation
- tool - if you use a tool you will speed-up the implementation
- organizational set-up - depending on complexity of your company, length of the implementation can vary (usually, bigger organizations need more time).
- people - this includes people that you have (number of supporting employees/customers, as well as people you can involve in incident management process).