How to disambiguate printed clock times from printed duration times?

I'm working on an app that allows users to construct timelines (kind of like events in calendars). But the timeline/sequence is independent of any specific datetime to execute, so all of the times in it are durations/offsets.

However, some users come with predisposed ideas that they'll be building these timelines in "real clock time". I've struggled with a mechanism to steer them clear of that model. Like the times printed down the left side here, part of the problem that allows them to confirm their incorrect conclusion, is that we tend to print/show clock times (e.g. 8:30) the same way that we do as an 8 hour 30 minute offset/delay (i.e. 8.30).

Is there a design language I've missed over that better differentiates printed durations vs printed wall clock times?