They have different but similar meanings. “Can” take hours in the first sentence means that it may take an hour but it may not. “Sometimes” in the second sentences also means that it may take an hour but it may not. “Sometimes” is different however because it implies that the ceremony is completed under an hour more often than not.

They almost mean the same thing. The second sentence though implies that normally there is a 'standard' time that the ceremony takes but sometimes it goes over that (due to xyz happening).

The two phrases have slightly different meanings. The first phrase, “The ceremony can take hours to complete,” expresses that the ceremony is able to take hours, but does not actually state whether or not the ceremony has taken several hours to complete in the past. It just states that it is able to do so. By contrast, the phrase, “The ceremony sometimes takes hours to complete,” expresses that the ceremony historically has taken hours to complete. I would also like to mention that while you may hear native speakers say the first phrase, it is better to use the words “is able to” instead of “can.” I would thus say for the first phrase, “The ceremony is able to take hours to complete.” I hope this helps. :) If you would like to practice speaking, please feel free to look at my teaching profile and class offerings. Kristin https://www.italki.com/kagcafe

Hi, Makoto! Zack's answer is correct. I just want to add that, in usage, the first sentence is more often used to predict what could happen, whereas the second sentence is usually used to describe what has happened based on past results.

Yes, both "can" and "sometimes" are being used to modify the certainty of the sentence. They both mean the same.