I'd like to thank everyone for all the great advice I've already gotten here, I'm hoping you'll indulge one more question. The Rick Steves guide recommends hitting the three attractions above prior to hitting Palacios Nazaries. I'm wondering how much time on average should one allow for doing that? Given the relatively strict ticketing policy for entry to the latter (and the possibility of a line), I'm a bit paranoid about missing my appointed time.
Earlier this year, I missed my visit to a 78 € Happy Hour visit to the Vatican due to a bit of miscommunication and I'm rather determined to avoid a repeat here.