At zero remaining seconds, this toy cache treats the answer as expired.
At zero, the answer expires
After 300 seconds, remaining TTL is 0.
300−300=0
Zero is not valid here
This toy table marks zero remaining seconds as expired.
valid=0
Expiration is not a new address
The answer address bytes are unchanged; only the cached freshness reaches zero.
remaining=0
Summary
A cache can use the answer while remaining TTL is positive; at zero, this toy row is expired.
remaining=0