Here are the steps we took to solve the challenge:
i open link
this is a epoch and unix date time convertor convert milisecond to date
no normal ls or cat input accespt so i used 123&&ls and it run both and get flag.txt
iuse 123&&cat flag.txt and get flagnite{b3tt3r_n0_c5p_th7n_b7d_c5p_r16ht_fh8w4d}