Yes, observations are just going into court to observe the business of the day. Pick different days of the week, as this gives you the best chance of seeing different work on the two days. For example, my home court does Remands every day, but traffic on Fridays only. You might not see a trial, but will almost certainly see the management of cases, and a good deal of sentencing.
Courts are public buildings, so you can go at any time; my advice would be to go straight to the ushers’ desk/office, explain why you’re there, and ask for their help/guidance. They’ll know which courts are likely to be busiest, but also the courts where mags are sitting, rather than a judge. I would aim to be there from 9.30 (court starts at 10, but worth getting there earlier to get yourself in and settled) until lunch, which is usually 1. At that point, I’d take a view about the afternoon; if you’ve seen a busy morning with a variety of cases, you might well want to leave it at that.
Just make a note of the dates, you’ll need to mention them on your application; I’m pretty sure the dates won’t be checked. That said, I would expect at least one of the interviews to touch upon your observations, for example what you saw and your thoughts.
Good luck, hope all goes well.