For combo sites you have two days to visit the combo sites. For the colosseum you can visit either the colosseum or the forum/palatine hill site first and then visit the other either later that day or the next day. All visits must be made during the validity of the pass and you can only enter each site once.
- Should I buy romapass online or wait until getting to Rome?
- What sites at the Vatican are covered by the romapass?