There are two causes of failures. First, if the two dates are joined at different milliseconds, then they will inherit different millisecond values during d:join, unless the full 10 items are specified in the array.
Second, there is a bug with
d:+msec in 8th version 23.06 (I believe since in 23.02 https:/8th-dev.com/bin/bugs/tktview/b82069cc12), causing the time to change by the value of the local time zone. If your time zone GMT you won’t notice. It is fixed for the next release (23.07?).