MIDI tempo adjustment?

Any thoughts on the best way to do this?

My audio source fills a MidiBuffer in the getNextAudioBlock() call*. The MidiBuffer is populated by getting a MidiEventHolder from a MidiSequence. Is it simply a case of calling addTimeToMessages() on the sequence? If so here's the really dumb question: what units are used here? For example to reset the tempo from 120 to 60, would delta be 2.0? convertTimestampTicksToSeconds() has been called on the source MidiFile once it is opened.


*Possibly not ideal to read stuff from disk at this point but it'll do for an experiment.