Martin (1992: 185):
External temporal relations are strongly oriented to the activity sequences constituting fields. Most of these relations (excepting co-extensive simultaneous ones) have the experiential structure Anterior · Posterior, where Anterior names the event which begins before the Posterior.
At primary delicacy the opposition is between [successive] relations, where the Anterior does not continue beyond the beginning of the Posterior, and [simultaneous] relations, where the two events overlap to some extent. This is the opposition between after and while in [4:24] and [4:25]:
[4:24] After we walk the ring with our dog,
we just wait.
[4:25] While the judge is handling the dog,
we hope that it will stand nice and steady.
 Here an experiential structure is proposed for a logical structure — a clause nexus.
 The temporal relations exemplified are between clauses in clause complexes. The grammatical categories are:
- same time A meanwhile B
- different time: later A subsequently B
- different time: earlier A previously B
¶ In modelling logical relations between clauses, this is simply rebranding Halliday's grammar as Martin's discourse semantics.