I've heard a lot of amplifiers reviewed and critisized on their 'timing'.
Although not an expert, I'm fully aware this cannot mean 'pitch'. No amp is going to 'speed up' or 'slow down' a recording in real time, so common sense tells me it's something to do with the pace of the high and low feguencies in a particular snippet of sound - keeping up with each other to produce an acurate sound for each note?