We will be in Bologna in the first week of March, and plan to visit Ravenna on Wednesday, March 5, to see the mosaics. That day is Ash Wednesday, the start of the season of Lent. Do you know if there are likely to be restrictions on visiting Ravenna churches on such important days in the Catholic church calendar?
You might try emailing the official site
https://www.ravennamosaici.it/en/
If you know you definitely want to visit on March 5, then I suggest you go to the website Christine listed above and check the availability of tickets for that day. If tickets are available and you reserve them now, then you are set. Even if there aren't restrictions, tickets may sell out for some churches. My experience last October was that one of the 5 sites for the combo ticket was fully booked for the date I originally wanted so I changed them all to the next day and was able to reserve. I did this only a couple days in advance but it was a non-holiday mid-week day. Advanced reservations are not required but without them you risk not getting in to some or all of the sites covered by the combo tickets. There are also one or two additional churches outside the center of Ravenna that are not covered by the online combo ticket.
Thank you both so much, Christine and CD! I appreciate your prompt replies and direction to the website. I was remiss in not having searched that out myself! Your experience of the combo ticket and changing dates, CD, is very helpful advice. Many thanks!!