We planned to visit Vatican Museum on a Monday morning. Just checked the online reservation and found out only the 12pm appointment is available. So after reading Ron's article about Vatican prebook, it seems like there is no need since there will be less crowd around noon. Also RS suggests to visit the museum around 3pm.
How much time will visiting St. Peter's Basilica take if we start in the morning like 8am? Where else to go before heading to the museum around 1pm or 3pm? Unfortunately the Castle Sant Angelo is not open on Monday, otherwise it'll be a good place to spend 2-3 hrs.
Is there enough time to visit Santa Maria del Popolo or the Spanish Steps and then come back to visit the museum?