Martin (1992: 180-1):
The distinction between external and internal is probably clearest with temporal relations. External relations are used to display the activity sequences in which people engage as members of various institutions. Internal relations on the other hand attend to text-time — time in relation to what is being said, not what is being done. In certain registers, especially those where language accompanies what is going on institutionally, text time and field time are so much in tune that the internal/external distinction is not that important.
 This confuses the ideational metafunction with the textual metafunction. External temporal conjunctive relations do not 'display the activity sequences in which people engage as members of various institutions'. External temporal relations, like all conjunctive relations, are cohesive resources for marking textual transitions between messages or groups of messages. These relations are distinct from the messages thus related.
 In SFL theory, 'text time' is the temporal dimension of logogenesis; 'field' is the ideational dimension of context, the semiotic system that has language as its expression plane. As a text unfolds during logogenesis, so too does the instance of context (field, tenor and mode) that the text realises.