The Unix epoch is the point where time starts for many computer systems — 1970-01-01T00:00:00Z. Unix time (a.k.a. epoch time or POSIX time) usually counts the number of seconds (or milliseconds) that have elapsed since the epoch.

# seconds -> readable (Python)
import datetime
ts = 1690000000
dt = datetime.datetime.utcfromtimestamp(ts)   # use .fromtimestamp for local time
print(dt.isoformat() + 'Z')

# readable -> seconds
import time, datetime
s = '2023-07-01T12:34:56'
# parse as naive local time example
dt = datetime.datetime.fromisoformat(s)
epoch_seconds = int(dt.timestamp())

# milliseconds example
ms = 1690000000000
seconds = ms // 1000