daylight saving related negative time will be an issue if a work period starts a the time auto daylight changes. That happens generally at 2-3 am and I never heard that caused an issue somewhere.
It is still vulnerable to manual time changes back and forth while SambaPOS working. There is no full coverage solution other than relying Internet time. Discussed that before and instead of requiring permanent Internet connection we thought the best solution will be limiting user permission to change system time.
For a regular operation that will never happen because of daylight saving.
-51 minutes only possible if I start a work period at the time daylight saving changes and end it 9 minutes later. For a normal operation that will be -1 hours. If it is 10 hours in a regular day it will be 9 hours. Never become negative for work periods open for more than 1 hour.
That should be something else as daylight saving will start at the end of the month. That might be manual time adjustment or time was already wrong and internet time corrected it.