What's the most efficient way to run: 4 on and 4 off, or 13 and 8. Also, do I need to indicate a shift start time on the log sheet?
Asking about the most efficient way to run, is an interesting way of approaching the issue.
First of all, the science on fatigue, sleep deprivation and behavior strongly suggest that a full eight hours of sleep, slightly more or less depending on the individual, is required to fully restore the body and mind to a rested state after a period of wakefulness of about 16 hours. That evidence is pretty clear. When you run 4-on and 4-off, what you are really doing, from a scientific point of view, is napping. The body doesn't cycle through all of the necessary phases of sleep during a four-hour period, therefore isn't properly rested.
If you're looking at efficiency from a driving point of view, 4-on and 4-off doesn't give you any more driving time in a 24-hour period, in fact, it will cost you 4 hours of driving time. Running in Canada, you're allowed 13 hours of driving per shift. As an example, starting at midnight, you can drive, theoretically, until 1:00 in the afternoon, then you take 8 hours off, then you may drive an additional 3 hours, as part of the next shift, before midnight. This gives you a daily total of 16 hours. That's legal.
The following day, you have 5 hours available from the shift you began before midnight, then 8 off, then 11 hours more driving before midnight, for a total of 16 hours again. On and on it goes until you run out of hours on the weekly cap.
The 4-on and 4-off allows you to split the sleeper shift, which is sometimes used to log actual on-duty time, such as loading, as sleeper time. This is illegal, but the split sleeper shift provision makes it technically possible. Also, this method makes it very difficult to keep track of on-duty vs. off-duty time, especially when calculating the total rest time required over a 7 day period. It's a ticket looking for a place to happen.
When considering efficiency, you should always place your body's need for the proper rest ahead of any other consideration.
As far as the start-time requirement is concerned, it's still in the regulations but it's widely disregarded. If the field on the log sheet is left blank, the assumption will be that your shift-start time is midnight. If you indicate a start of say, 8:00 AM and you show on-duty hours before that, you're in violation. My advise: Leave it blank.