Navistream calculates Deferral Time automatically.

Canadian Federal HoS Rules state the Driver needs to take at least 10h off duty time in a day with 8h of that time being consecutive (unless using split-SB Rules). Off duty time is only counted in blocks of >=30min. So, If the Driver takes <10h but >=8h, they will need to 'pay back' that outstanding off duty time requirement the following day.
Note: Sleeper Berth duty status is considered off duty time. 

Here's an example:

Day 1

  • Driver takes 8h consecutive Off Duty
  • No other off duty time is taken

Day 2

  • Driver logs in and sees that they have 0h Deferral remaining and only 12h Drive and On Duty time
  • Driver needs to take 12h total off duty time in the day (instead of 10h) with 8h of that time being consecutive (which means 4h off duty time during their day counted in blocks >=30min.)

Please refer to the following Canadian Federal rule: