Flydream, in my experience it was left completely up to us to decide when to come. Most people arrived a couple of days early to recover and get their bearings. Some crazy people arrived just the night before. Your 30 days accommodation on the company start from whenever you arrive. Just pick your flights and ask your joining coordinator for them.
Medical starts straight away, I think. But there's always a grey area before you've got your residency visa stamped. Once you've got that, you're definitely covered. Usually takes a week or two depending on how much/little the government offices are working. If you're arriving during Ramadan, things might take a few more days...