IMU data processing in Ros

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I've successfully connect my libfreespace with ros and I successfully build up the connection between publisher and topic. But the problem is that the time interval between two data is not the same and my tutor advised me to use a buffer. For example, the time interval is approximately 0.008s , I get a buffer of 0.02s and generate a vector and publish it to the topic. But how can this be done? And another problem is that I use 2 imus so the Synchronization is a problem, my idea is that one IMU data can start faster than the other so we don't use the first several data. but how can it be done? I use the ros header time stamp of current time to record the time.