I'm relatively new to the company, so I would love to understand more about this. Here's more specific questions I had:
There is a grace period for new employees. The ramp up will depend on the team, level, and domain, but in general you can expect PSC to not be as harsh for your first cycle. By default, you'll get the MA (meets all) rating if you only have a few months left in the half, unless you've gotten some strong feedback that something is off. Since you're a senior eng, this is probably fine, but for E3/E4 engineers, I usually tell them to aim for a higher rating even in the first half, if promo is really important to them.
Generally the evaluation will start when you are placed on a team. The way PSC works is that your manager will collect the work/impact you did on the team since you joined, and make a case for what rating you should get. Most managers won't look at your bootcamp period unless it was very long.
I think this is totally fine, especially if you're new to the company. A lot of the delayed impact relies on understanding the context + business needs, which takes time to understand. The way I'd think about it is, "how strong is my narrative that I laid the groundwork for impact in a later half?" The concern would be if you think you did a bunch of work for a future half, but no one actually gives you credit for it.
These are great questions and I'd encourage you to have a frank discussion with your manager. If your manager is not good/new, they may not be sharing their expectations for your ramp up, so it's your job to ensure you have clarity around the expectations.