If I finish a session ahead of time can I skip to the following one?

You know it may also be beneficial for your focus (and to keep you from rushing yourself) to use any extra time to sort of just chill out and unwind yourself from the last hour+ of focusing. If you spend the ENTIRE test ultra focussed you're more likely to tire yourself out than if you relax as often as possible (given breaks and extra time).

For me if it's for example 5 minutes over, I'll spend 1-2 writing stuff down for the next section (like factor trees, things that will save time to revert back to), a couple minutes just closing my eyes and slowing down, and then the final minute or so I turn around and wait for the test proctor to be available to take me for my break.

The last part can be important if, like my test center, your test center is filled with ancient slowpokes who seem to think they'll cause a fire if they move faster than a stationary rock. I've taken the test a couple times and the first about 4 breaks I started a minute late and got signed in about two minutes late because of how slow the proctors were so I realized if I had extra time it was beneficial to wait to advance to the break at the optimal moment.

Just my two cents.