I'm not entirely sure what your overall goal is, with that in mind.
Assuming that AB153D
are hex representations of linux epoch (seconds from January 1, 1970), have a look at this:
# hex input is 521dd201:
date --date @$( printf '%d\n' 0x521dd201) '+%Y-%m-%d %T'
# hex input is Ab153d
date --date @$( printf '%d\n' 0xAb153d) '+%Y-%m-%d %T'
The printf part converts from hex to decimal, which leaves you with epoch in seconds. This epoch can be given to the date command (--date @no_of_seconds), the last part ('+%Y-%m-%d %T') specifies the wanted output.
See the date manual page for details.