Add 20 minutes to the current date.
date --date 'now +20 mins'
Add 4 days 2 hours 14 mins from 2020-08-17 22:00:00
date --date "2020-08-17 22:00:00 4 days 2 hours 14 mins"
Subtract 5 minutes from the current date.
date --date 'now -5 mins'
Add 4 days 2 hours 14 minutes and return it in unixseconds.
date --date '2020-08-17 22:00:00 4 days 2 hours 14 mins' +%s
And subtract 4 days 2 hours 14 minutes and return it in unixseconds
date --date '2020-08-17 22:00:00 4 days ago 2 hours 14 mins' +%s