Fix the behavior of TTL

The 30 day TTL limit before interpreting TTL as a UNIX timestamp
is incredibly unintuitive and prone to create bugs. Instead, only
interpret this value as a UNIX timestamp when it's remotely in the
range of being a valid UNIX timestamp. I chose the timestamp of
the date this project was started. Assuming system time is correct,
this is a backwards compatible change for those who use timestamps
as TTL but now allows for TTLs greater than 30 days (in fact, up
to ~32 years)