There are many new clients using CA Datacom who may not have dealt with the time change from Daylight Savings time (or Summer time) back to Standard time, and while the problems associated with this change become less and less over time, there are a few things you can do to make this change more successful.
Here is an overview from a TEC document titled "DST Instructions for CA Datacom/DB and CA Datacom/AD," which can also be found by searching for TEC433738.
For the change from DST back to Standard Time, the only area of concern with CA Datacom/DB is in performing a recovery using log records from this overlapping hour of time, should that be necessary. The same would be true for a CA Datacom/AD environment if you are doing RECOVERY function processing in your AD region. However, many products from CA that use AD do not require the use of the RECOVERY function.
The CA Datacom log records that are stored in the Log Area/Recovery Area (LXX/RXX) contain both an external date-time and astore clock value. Since the log does not allow a date-time step down, special care must be taken in RESTART or RECOVERY processing if performed across the time change boundary. For example, recovery should not process tapes with data that spans the time change boundary; recovery may need to be run twice -- once with the RXX from prior to the time change and a second time with the RXX from after the time change.
Until TIME_SYNC was introduced, at the end of Daylight Saving Time, all CA Datacom users had to either recycle their MUF region or accept that the MUF date-time would be wrong from the point of the time change until the region was next recycled. But, with TIME_SYNC, the process eliminates the recycle of the MUF region and immediately makes use of the new time.
Please refer to the TEC document above for details about the process to follow for z/OS and z/VSE.