Use when if you're tying an action to a real point in time, and the when-clause needs a main clause: When I start the new job, I'll update my email signature. Keep present tense inside the clause, so When I start, not When I will start.
For a first day at work, the time is real: When I get my desk assignment, I'll set up my laptop.
If the time isn't fixed, switch to if: If we confirm Tuesday, I'll send a calendar invite.
First day in a new job
First day at work: you're tying the action to a real point in time, so when fits and needs a main clause to complete its meaning. When I get my desk assignment, I'll set up my laptop. The when-clause can't stand alone; it hangs onto the main clause.
Telling a colleague about your schedule: the event has a known time, so use when with present tense even for the future. When the team meeting starts, I'll introduce myself. Don't say When the team meeting will start; will stays out of the when-clause.
Contrast: if the time is uncertain or you're imagining a possibility, shift to if instead. If you're free on Tuesday, we can confirm the interview time. Once the Tuesday time is actually fixed, when becomes the right choice for wording like that.
Confirming an interview time by email
If the day isn't actually fixed yet, you're talking about a possibility, not a time, so if is the natural choice. If we can confirm Tuesday, I'll send a calendar invite. With when, you'd sound like the Tuesday meeting is already settled.
Once the time is agreed, switch wording: When we confirm Tuesday, I'll send the invite. The decision comes down to a real point in time versus an open possibility, and your reader can hear the difference in your confidence.