I tried to do some initial research, but other than clarifying that Rams are generally for Walls not Gates, I wasn't able to determine any specifics regarding timeframe for breakthrough.
I might assume the Romans might keep detailed enough records if it takes a long period of time, they would track the progress of the Ram over the course of days; and the lack of such records might imply it would do the work within a short period if it wasn't stopped, such as within a single day. However, this seems like a dangerous assumption to make.
The goal for this question is to design a classical era siege game, and I need to figure out if Rams were more "strategic level" weapons you deploy over the course of days or weeks, or a tactical level breach generator you send with your troops on the main assault.
Hi there - we're happy to approve your question related to your creative project, and we are happy for people to answer. However, we should warn you that many flairs have become reluctant to answer questions for aspiring novelists and the like, based on past experience: some people working on creative projects have a tendency to try to pump historians for trivia while ignoring the bigger points they were making, while others have a tendency to argue with historians when the historical reality does not line up with what's needed for a particular scene or characterization. Please respect the answers of people who have generously given you their time, even if it's not always what you want to hear.
Additionally, as amazing as our flair panel is, we should also point out that /r/AskHistorians is not a professional historical consultation service. If you're asking a question here because you need vital research for a future commercial product such as a historical novel, you may be better off engaging a historical consultant at a fair hourly rate to answer these questions for you. We don't know what the going rate for consultancy work would be in your locality, but it may be worth looking into that if you have in-depth or highly plot-reliant questions for this project. Some /r/AskHistorians flairs could be receptive to working as a consultant in this way. However, if you wish for a flair here to do this work for you, you will need to organize this with them yourselves.
For more general advice about doing research to inform a creative project, please check out our Monday Methods post on the subject.