Using Template in Developer tools I did this
CleanStart:{{ as_timestamp(state_attr('vacuum.xiaomi_vacuum_cleaner','clean_start')) | timestamp_custom('%a %d %b at %H:%M') }}
CleanStop:{{ as_timestamp(state_attr('vacuum.xiaomi_vacuum_cleaner','clean_stop')) | timestamp_custom('%a %d %b at %H:%M') }}
CleanTime:{{ (as_timestamp(state_attr('vacuum.xiaomi_vacuum_cleaner','clean_stop')) - as_timestamp(state_attr('vacuum.xiaomi_vacuum_cleaner','clean_start'))) | timestamp_custom('%H:%M') }}
Results in:
CleanStart:Fri 01 Jan at 15:56
CleanStop:Fri 01 Jan at 16:46
CleanTime:10:50
What is going on with the timestamp subtraction?
I am 10hrs ahead of UTC in Sydney, Australia but I just don’t get it.