Thanks for the quick reply - I saw that link already but I don't think it helps in my case as I need to use a combination of time types e.g.
90 seconds = 1 minute 30 seconds.
So I would need to convert the 90 seconds into 1.5 minutes (which I can do from the custom scaling approach) but then identify that 0.5 minutes = 30 seconds and then return 01:30.