For a long time, no one commented accurately on what these codes signify. By the time this D8 cancellation came into usage between 1910 and 1913, Labuan had already joined the Straits Settlements in January 1907. Similar letter codes were seen in the Straits cancellations and these were time codes but whether they were used accurately is opened to debate. Logically code A would represent the earliest time period in the day and code E the latest. Code E is difficult to find and it may have been that it was used during a quiet late period, for instance when a ship arrived during the night.
Time codes A & B on Straits stamps. This postmark can also be found on Brunei or North Borneo adhesives.
It is not common to find this cancellation on a Brunei stamp. We have the time code C here. Its usage would represent paquebot use or a transit cancel. The bulk of mail from Brunei went through Labuan during this period as there were regular ships plying the route between Singapore and Labuan.
This is code D on a pair of of North Borneo stamps and probably represented paquebot mail from the south western part of North Borneo near to Labuan and would have been more efficient than going through the GPO at Jesselton. It could also be possibly an an arrival or transit cancel.
Time code E is quite difficult to obtain and probably even more unusual to be seen on a pair of North Borneo stamps. Were both these pairs of 4c adhesives used for books or printed matter for an item weighing 8oz?