Not sure if I understood your question clearly but when setting up an RFP, you decide for how long would you keep the event available to the participant to respond to (Response start & due dates).
If you are referring to the questions that the participants have with regards to the event content, then in my opinion, when an RFP is 'Open' to the participants, they can use the 'Compose Message' feature to send messages to the project team. If other methods of communication like chat or phone are used, then it is recommended that you keep a log of what has happened by announcing it through 'Message Board' (Project view) or send messages from within the event.
Hope this helps.
I'd second this and highly recommend you use the Ariba messaging feature. When you get a question in, you can respond to all participants so that all suppliers have the same information at the same time. (Make sure to read through the original message and delete any identifying information.)
From our experience using messaging area from Ariba to have track of all Q&A has result one of the best practices, since it allows you to centralize all information. I agree with Tim in regard to respond to all suppliers about the questions received. What we have done is to collect all Questions and at the end of the day answer all to all suppliers trhough Ariba System.
Q&A period should be mentioned at the conditions of your event so suppliers can know clearly how long is this period. Also Q&A should change depending of the category you are sourcing, it is not the same time of Q&A for a construction bid than for raw materials.
We used to open Q&A the same day the invitation has been issued and close it one or two days before pre bid.
Hope this will be helpful for you.
Thanks all for your valuable input. You've answered my question.