The Carts use local time so that there is no time translation process to consider to interpret when a cart actually occurred relative to local time. However, this introduces an issue when Daylight Savings Time is used.
The XML time in the cart does contain the time zone offset, from which you can see the difference between two times that are essentially the same but one being Standard Time and the other being Daylight Savings Time. However, this is of limited use.
There is no major issue during all hours but two during the year, the transition hours. Of those two, one is a lost hour and essentially has no impact. There is an issue when considering things like totals for a day since that is a 23 hour day. Since this transition time is typically 2AM, in most cases this hour is barely or not used.
The hour of concern is when the 2AM hour repeats in local time. In that case it is possible for a cart to be generated at 2:34:56 and then an hour later, after the time is shifted, for another cart to be generated at 2:34:56.
Because the Cart’s identifier contains both the time and a random sequence number that is guaranteed not be duplicated, each cart generated at the same second, but an hour apart, will be unique.
Since you effectively have a 25 hour day, from the local time perspective, averages or totals for the day may be affected. However, this is greatly mitigated in most cases due to the typically quiet 2AM hour.
There is the possibility of a cart at 2:55AM and then another, 10 minutes later after the shift at 2:05AM. When listed, they will not appear in the actual order of occurrence, since 2:05 is normally before 2:55.
The ideal solution is to eliminate Daylight Saving Time, but since this is a legislative process and not software, we will not address it here.