When I finished University
This is used to talk about the past, since you're using the past tense: "finished"
When I finish University
This can be used to talk about a planned future.
Example: "When I finish University, I'll move out."
This means I will move out when (usually the moment) I finish University.
When I have finished university
This is present perfect tense. This would be the best option for your situation.
Example: "I'll get a job when I've finished University."
This means I plan to get a job some time after having finished University.
While the second case (finish) tends to point to a short time (often a moment) right after the action (finish University), the third case tends to point to any time after the action, which means it can be 2 years after finishing University.