Found it! For anyone else who needs to know: Go to Options, Display and select 'Time elapsed'. In both 'Time format' and 'Duration' select "hh.mm.ss (with leading zero)".
Worked first time!
Apologies if this has already been covered - Is there a way to change time code formats so it shows as 00:00:00 and not the default format? I am working on some long documents. One has to be time coded every few minutes and I'm having to change it manually.
Many thanks in advance...