How can I create an IC4 -> IC5 growth plan?

Time is a secondary factor compared to gap analysis and plans to fill them. Your plan may have hard time blocks (to launch a thing and maintain it, show success may take a few halves), but saying “I want to be promoted in 2 years” will still just come back to your gaps and seeing how to fill them in 2 years.

With the help of a manager (doesn’t have to be yours) or an engineer that has provided feedback on a successful IC5 promo, go through the guidelines for that level, and give examples of what you’ve done that meets them. If you have none, that goes right onto the gap list. If you have weak examples, it can go into a “needs improvement” gap section. Then start ideating. Is it people things? OK, do you need to mentor someone? Do you need to shepherd a promotion from L3 -> L4? Maybe it’s project ambiguity… get involved in your team’s planning and identify what projects are poorly defined and work with your manager to take ownership of those things. Once you have a plan, maybe missing a couple of pieces, work with your manager to see if they agree on the action items filling the gaps, and ask for support in filling them. If you haven’t found ideas to fill all the gaps, be looking and asking others.

Note checking all the boxes won’t mean you get promoted, but if you don’t you almost assuredly won’t.