Aritmetic operation on Cron pattern -

i have use case need schedule 2 tasks 1. @ 'x' time defined cron pattern 2. @ 'x minus 2 hours' need calculate cron pattern based on first cron pattern

for eg if first task scheduled @ 1 o'clock everyday 0 01 * * * find out first task time minus 2 hours, 0 23 * * *

please suggest on how can achieved.