Asked a similar question a while ago...this is the answer I got from "one in the know"....
The answer is not simple. Where a DME dependent approach has a DME limiting base turn this figure is shown on the plan graphic. Example Tauranga NDB/DME RWY 07 where 7 DME is shown on the plan graphic. A distance figure is not shown on the plan graphic for the NDB/DME RWY 25 approach so time only applies when flying the base turn.
The 7.3 DME annotation is the distance at which an aircraft at 2000ft will intercept the 2.9° (5%) descent angle and is not the limiting distance for flying the base turn procedure.
I accept it is confusing and this is an issue that the chart standards working group is trying to overcome. Introducing constant angle descent profiles (AIC 5/05 refers) looked easy at first but there are some fish hooks. The Tauranga NDB/DME RWY 25 approach was one of the early charts changed and I believe is to be amended again.
Why a DME dependent approach has outbound timing and not distance is one I can't answer.
Clear as mud??
(NB Asked the question back in FEB 07 so the quoted plates may have moved on since then!)